Distortion and aliasing reduction for digital to analog conversion

ABSTRACT

Distortion and aliasing reduction for digital to analog conversion. Synthesis of one or more distortion terms made based on a digital signal (e.g., one or more digital codewords) is performed in accordance with digital to analog conversion. The one or more distortion terms may correspond to aliased higher-order harmonics, distortion, nonlinearities, clipping, etc. Such distortion terms may be known a priori, such as based upon particular characteristics of a given device, operational history, etc. Alternatively, such distortion terms may be determined based upon operation of a device and/or based upon an analog signal generated from the analog to conversion process. For example, frequency selective measurements made based on an analog signal generated from the digital to analog conversion may be used for determination of and/or adaptation of the one or more distortion terms. One or more DACs may be employed within various architectures operative to perform digital to analog conversion.

CROSS REFERENCE TO RELATED PATENTS/PATENT APPLICATIONS ProvisionalPriority Claims

The present U.S. Utility Patent Application claims priority pursuant to35 U.S.C. §119(e) to the following U.S. Provisional Patent Applicationwhich is hereby incorporated herein by reference in its entirety andmade part of the present U.S. Utility Patent Application for allpurposes:

1. U.S. Provisional Patent Application Ser. No. 61/433,128, entitled“Method to extend the dynamic range of a digital-to-analog converter(DAC),” filed Jan. 14, 2011.

Incorporation by Reference

The following U.S. Utility Patent Applications are hereby incorporatedherein by reference in their entirety and made part of the present U.S.Utility Patent Application for all purposes:

1. U.S. Utility patent application Ser. No. 13/118,429, entitled“Imbalance and distortion cancellation for composite analog to digitalconverter (ADC),” filed May 29, 2011, pending, which claims prioritypursuant to 35 U.S.C. §120, as a continuation, to the following U.S.Utility Patent Application which is hereby incorporated herein byreference in its entirety and made part of the present U.S. UtilityPatent Application for all purposes:

2. U.S. Utility patent application Ser. No. 12/949,752, entitled“Imbalance and distortion cancellation for composite analog to digitalconverter (ADC),” filed Nov. 18, 2010, now issued as U.S. Pat. No.7,952,502 B2 on May 31, 2011, which claims priority pursuant to 35U.S.C. §119(e) to the following U.S. Provisional Patent Applicationwhich is hereby incorporated herein by reference in its entirety andmade part of the present U.S. Utility Patent Application for allpurposes:

2.1. U.S. Provisional Application Ser. No. 61/392,604, entitled“Imbalance and distortion cancellation for composite analog to digitalconverter (ADC),” filed Oct. 13, 2010.

The U.S. Utility patent application Ser. No. 12/949,752 also claimspriority pursuant to 35 U.S.C. §120, as a continuation-in-part (CIP), tothe following U.S. Utility Patent Application which is herebyincorporated herein by reference in its entirety and made part of thepresent U.S. Utility Patent Application for all purposes:

3. U.S. Utility application Ser. No. 12/453,431, entitled “Analog todigital converter (ADC) with extended dynamic input range,” filed May11, 2009, now issued as U.S. Pat. No. 8,009,075 B2 on Aug. 30, 2011,which claims priority pursuant to 35 U.S.C. §119(e) to the followingU.S. Provisional Patent Application which is hereby incorporated hereinby reference in its entirety and made part of the present U.S. UtilityPatent Application for all purposes:

3.1. U.S. Provisional Application Ser. No. 61/136,353, entitled “Analogto digital converter (ADC) with extended dynamic input range,” filedAug. 29, 2008.

4. U.S. Utility application Ser. No. 10/879,673, entitled “System andMethod for adjusting multiple control loops using common criteria,”filed on Jun. 29, 2004, now issued as U.S. Pat. No. 7,961,823 B2 on Jun.14, 2011, which claims priority pursuant to 35 U.S.C. §119(e) to thefollowing U.S. Provisional Patent Application which is herebyincorporated herein by reference in its entirety and made part of thepresent U.S. Utility Patent Application for all purposes:

4.1. U.S. Provisional Application Ser. No. 60/576,371, entitled“Dithering algorithm system and method,” filed Jun. 2, 2004.

5. U.S. Utility application Ser. No. 10/880,959, entitled “High speedreceive equalizer architecture,” filed on Jun. 30, 2004, now issued asU.S. Pat. No. 7,623,600 B2 on Nov. 24, 2009, which claims prioritypursuant to 35 U.S.C. §119(e) to the following U.S. Provisional PatentApplication which is hereby incorporated herein by reference in itsentirety and made part of the present U.S. Utility Patent Applicationfor all purposes:

5.1. U.S. Provisional Application Ser. No. 60/576,176, entitled “Highspeed receive equalizer architecture,” filed Jun. 2, 2004.

6. U.S. Utility application Ser. No. 12/269,865, entitled “Method andsystem for digital video broadcast for cable (DVB-C2),” filed on Nov.12, 2008, which claims priority pursuant to 35 U.S.C. §119(e) to thefollowing U.S. Provisional Patent Application which is herebyincorporated herein by reference in its entirety and made part of thepresent U.S. Utility Patent Application for all purposes:

6.1. U.S. Provisional Application Ser. No. 60/987,371, entitled“DVB-C2,” filed Nov. 12, 2007.

7. U.S. Utility application Ser. No. 13/223,094, entitled “Distortionand aliasing reduction for digital to analog conversion,” filedconcurrently on Aug. 31, 2011, pending.

8. U.S. Utility application Ser. No. 13/223,156, entitled “Distortionand aliasing reduction for digital to analog conversion,” filedconcurrently on Aug. 31, 2011, pending.

9. U.S. Utility application Ser. No. 13/223,182, entitled “Distortionand aliasing reduction for digital to analog conversion,” filedconcurrently on Aug. 31, 2011, pending.

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

The invention relates generally to communication systems; and, moreparticularly, it relates to imbalance and distortion cancellation forone or more digital to analog (DACs) as may be implemented withinvarious communication devices.

2. Description of Related Art

Data communication systems have been under continual development formany years. Generally speaking, a data communication system may beviewed as supporting the transmission of any of a variety of types ofinformation (e.g., data, voice, media, etc.) from a first location to asecond location within such a communication system. Communicationsystems are known to support wireless and wire lined communicationsbetween wireless and/or wire lined communication devices. Also generallyspeaking, within the context of communication systems that employvarious types of communication devices, there is a first communicationdevice at one end of a communication channel with encoder capability andsecond communication device at the other end of the communicationchannel with decoder capability. In many instances, one or both of thesetwo communication devices includes encoder and decoder capability (e.g.,within a bi-directional communication system). Transferring informationfrom one location to another can be applied generally within any type ofcommunication system, including those that employ some form of datastorage (e.g., hard disk drive (HDD) applications and other memorystorage devices) in which data is processed and/or encoded beforewriting to the storage media, and then the data is processed and/ordecoded after being read/retrieved from the storage media.

Certain communication systems employ one or more of various types ofcoding (e.g., error correction codes (ECCs) whose decoding may beperformed iteratively) to ensure that the data extracted from a signalreceived at one location of a communication channel is the sameinformation that was originally transmitted from another location of thecommunication channel. Communications systems with iterative codes areoften able to achieve lower bit error rates (BER) than alternative codesfor a given signal to noise ratio (SNR). ECCs, and the application ofECCs, are sometimes alternatively referred to as Forward ErrorCorrection (FEC) codes and coding. In modern systems, the terminology“FEC” can be applied to systems incorporating FEC but including partialor full re-transmission, perhaps with feedback from the receiver to thetransmitter based upon decoding success, decoding lack of success, orpartial decoding results (e.g., in accordance with U.S. Utilityapplication Ser. No. 12/269,865, entitled “Method and system for digitalvideo broadcast for cable (DVB-C2),” which is incorporated by referenceabove).

In addition, any of a variety of types of communication systems mayemploy one or more of various types of signaling (e.g., orthogonalfrequency division multiplexing (OFDM), orthogonal frequency divisionmultiple access (OFDMA), code division multiple access (CDMA),synchronous code division multiple access (S-CDMA), time divisionmultiple access (TDMA), etc.) to allow more than one user access to thecommunication system. Such signaling schemes may generally be referredto as multiple access signaling schemes.

In accordance with signals that are communicated within any of a varietyof communication systems, within a transmitter communication device,digital signals typically undergo conversion to continuous time/analogsignals for transmission or launching into one or more givencommunication channels. That is to say, one function that is oftentimesperformed in accordance with transmitting a signal from onecommunication device to another is to perform conversion from thedigital domain to the analog domain (e.g., using a digital to analogconverter (DAC)). Such a continuous time/analog signal is oftentimestransmitted via a communication channel from one location to another(e.g., from one communication device to another, from one location toanother location within a given communication device, etc.). Oftentimes,in accordance with performing such conversion from the digital domain tothe analog domain, the conversion process may sometimes be performedless than perfectly (less than optimally) such that a digital signal maynot sufficiently load the DAC.

For example, a digital codeword, when applied to a DAC for conversion toa corresponding analog signal, may underload the DAC such that anunacceptably low or insufficient power may be associated with the analogsignal, or too low a signal to noise ratio (SNR) may be associated withthe analog signal. And in even other situations, the conversion processmay sometimes be performed less than perfectly such that a digitalsignal may overload a DAC. That is to say, a digital codeword, whenapplied to a DAC for conversion to a corresponding analog signal, mayunfortunately extend beyond the linear and operable region of the DAC.In such situations, clipping and other nonlinear deleterious effects maybe realized in accordance with the conversion from the digital domain tothe analog domain. Even with near-optimal loading of a DAC, level errorsin the DAC output (e.g., the analog output does not replicate preciselythe relative numerical values attributed to the codewords input to theDAC) cause noise and harmonic and intermodulation distortion, as shownfor example when one or two (or more) sinusoids are generatednumerically and the DAC output is analyzed showing energy in theharmonic and intermodulation frequencies. Also contributing to the noisefloor and nonlinear distortion in a DAC output are level-dependentdifferences in analog component values, including compression atexcursions, sometimes not balanced or equal at positive and negativeexcursions. Phase noise or clock jitter in the DAC clocking signal alsointroduces distortion which can be characterized as intermodulationbetween the signal of interest (SOI) and the DAC clocking signal(including its phase noise or spurs).

In summary, the quantization of the numerically generated signals inputto the DAC are a source of some nonlinear distortion, but level errorsand nonlinear digital-word-value-to-analog-voltage-level transferfunction also typically contributes additional nonlinear distortion, andlevel-dependent artifacts typically contribute additional significantnonlinear distortion, especially in DACs operating with high clockingfrequencies. All of these nonlinear distortion mechanisms are typicallycontributing degradation, including nonlinear distortion characterizedby generation of harmonics and intermodulation products, even withoutsignificant clipping from overloading. Overloading or underloading theDAC input typically exacerbates some or many of these nonlineardistortion mechanisms, including increasing the rate and/or amount ofclipping distortion. Generally speaking, the prior art does notadequately provide for a means to address and overcome these and otherdeficiencies as may be experienced in accordance with digital to analogconversion within one or more DACs.

Within a communication device operative to receive a signal that hasbeen transmitted via a communication channel, the corresponding reverseoperation is performed in accordance with performing conversion from theanalog to the digital domain (e.g., using an analog to digital converter(ADC)). That is to say, one function that is oftentimes performed whenreceiving a signal is to perform digital sampling thereof (e.g., usingan ADC). When dealing with signals that may temporally vary across arelatively large dynamic range, performing such digital sampling can beproblematic and incur certain deleterious effects such as undesirablylow signal to noise ratios (SNRs) or undesirably large signal loadinginto the ADC. The prior art does not adequately provide for means toaddress and overcome these and other deficiencies as may be experiencedin accordance with analog to digital conversion within one or more ADCs.In addition, it is noted that while the term and/or terminology of“codeword” is utilized in both error correction code (ECC) and digitalto analog converter (DAC) related descriptions, the term and/orterminology of “codeword” has a different respective meaning for eachrespective application context (e.g., ECC vs. DAC related descriptions).

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 and FIG. 2 illustrate various embodiments of communicationsystems.

FIG. 3 illustrates an embodiment of digital to analog conversion.

FIG. 4 illustrates an embodiment of distortion synthesis for improvingdigital to analog conversion.

FIG. 5 illustrates an alternative embodiment of distortion synthesis forimproving digital to analog conversion.

FIG. 6 illustrates an embodiment of distortion synthesis, includingadaptation thereof, for improving digital to analog conversion includingimproving spurious emission performance.

FIG. 7 illustrates an alternative embodiment of distortion synthesis,including adaptation thereof, for improving digital to analog conversionincluding improving spurious emission performance.

FIG. 8 and FIG. 9 illustrate other alternative embodiments of distortionsynthesis, including adaptation thereof, for improving digital to analogconversion including improving spurious emission performance.

FIG. 10 illustrates an embodiment of distortion synthesis for improvingdigital to analog conversion including improving transition band and/orstopband performance.

FIG. 11 illustrates an embodiment of distortion synthesis, includingadaptation thereof, for improving digital to analog conversion includingimproving transition band and/or stopband performance.

FIG. 12 illustrates an alternative embodiment of distortion synthesis,including adaptation thereof, for improving digital to analog conversionincluding improving transition band and/or stopband performance.

FIG. 13 illustrates an embodiment of distortion synthesis for improvingdigital to analog conversion including improving skirt and/or spectralmask performance.

FIG. 14 illustrates an alternative embodiment of distortion synthesisfor improving digital to analog conversion including improving skirtand/or spectral mask performance.

FIG. 15 illustrates an embodiment of distortion synthesis, includingadaptation thereof, for improving digital to analog conversion includingimproving skirt and/or spectral mask performance.

FIG. 16 illustrates an alternative embodiment of distortion synthesis,including adaptation thereof, for improving digital to analog conversionincluding improving skirt and/or spectral mask performance.

FIGS. 17 and 18 illustrate other alternative embodiments of distortionsynthesis, including adaptation thereof, for improving digital to analogconversion including improving skirt and/or spectral mask performance.

FIG. 19 illustrates an embodiment of distortion synthesis, includingadaptation thereof and separately compensating for frequencies above andbelow, respectively, of a signal of interest, for improving digital toanalog conversion including improving skirt and/or spectral maskperformance.

FIG. 20 and FIG. 21 illustrate alternative embodiments of distortionsynthesis, including adaptation thereof and separately compensating forfrequencies above and below, respectively, of a signal of interest, forimproving digital to analog conversion including improving skirt and/orspectral mask performance.

FIG. 22 illustrates an embodiment of amplitude modulation-amplitudemodulation (AM-AM) characteristics and AM-phase modulation (AM-PM)characteristics.

FIG. 23 illustrates an embodiment of distortion synthesis, includingadaptation thereof, for improving noise power measurement as may beoperative to reduce dynamic range associated with power measurement ordetection or other frequency selective measurements employed therein.

FIG. 24 and FIG. 25 illustrate alternative embodiments of distortionsynthesis, including adaptation thereof, for improving noise powermeasurement as may be operative to reduce dynamic range associated withpower measurement or detection or other frequency selective measurementsemployed therein.

FIG. 26A, FIG. 26B, FIG. 27, FIG. 28A, and FIG. 28B are diagramsillustrating embodiments of methods for operating one or more devicesincluding at least one digital to analog converter (DAC) therein.

DETAILED DESCRIPTION OF THE INVENTION

Improvement in the performance of digital to analog signal conversion ispresented herein. Reduction of various deleterious effects as may beexperienced at both the upper and lower loading and reduction oflimitations associated with digital to analog conversion, may beachieved in accordance with performing digital to analog conversion inaccordance with various embodiments, aspects, and their equivalents, aspresented herein.

As the reader will understand, conversion from the digital to the analogdomain, such as may be performed within any of a variety of devices, mayunfortunately be performed less than perfectly (due to practicalrestraints and limitations) and may suffer from a number of effectsincluding spurious emissions. Generally speaking, one or more digitalcodewords are provided to one or more digital to analog converter (DACs)for generating one or more analog signals. It is noted here that suchterminology as continuous time signal, analog signal, etc. such as asignal that is output from a DAC, such as in accordance with the digitalto analog conversion of a digital signal, may be used interchangeably.For brevity in accordance with various illustrations provided herein,analog signal is oftentimes used.

Typically, a digital signal is provided to a DAC in the form of asequence of digital values, such as a digital bitstream, a sequence ofdigital codewords, a sequence of digital labels, etc. The individualrespective values within the digital signal are successively andrespectively applied to a DAC in accordance with generating an analogsignal. A DAC is operative to seam the successive digital values withinthe digital signal together thereby forming the analog signal.

When a digital codeword is provided to a digital to analog converter(DAC) for conversion from the digital domain to the analog domain, theconversion process may be performed less than perfectly due to theinherent limitations of a DAC. Ideally, the conversion process would beperformed linearly and perfectly for any given digital codeword.However, a typical DAC is operative to provide its best performance andits most linear performance within a certain range. When a digitalcodeword provided to a DAC is relatively large or reaching the upper endof the linear operating range of the DAC, the DAC may exhibit nonlinearcharacteristics including clipping in accordance with generating ananalog signal. When a digital codeword exceeding the linear operationalrange of the DAC is applied thereto, the corresponding DAC will exhibitnonlinear characteristics including clipping in accordance withgenerating an analog signal. At this top end of the dynamic range of agiven DAC, distortion may unfortunately be generated including thirdorder harmonics and intermodulation products (e.g., and sometimes,2^(nd) harmonics and intermodulation products and even higher orderharmonics and intermodulation products). When the digital codewordprovided to a DAC is relatively small or reaching the lower end of theoperational range of the DAC, operation of the DAC may be quantizationnoise limited. At the lower end of the operational range, nonlineardistortion also may be manifested due to the relatively coarsequantization step size associated with the digital codewords when only afew of the least significant bits are varying for a duration of time (ornumber of successive codewords).

In accordance with appropriate operation of signal conversion from thedigital domain to the analog domain, the operation of the DAC preferablywould not be underloaded (e.g., being quantization noise limited, notproviding an adequate output power, etc.) or overloaded (e.g., clipping,nonlinearity, distortion, aliasing, higher order harmonics, etc.).However, in real life applications, operation at or near the limitationsof various devices, including near saturation of a DAC in which such aDAC exhibits nonlinear characteristics, is oftentimes unavoidable.

A number of different architectures are presented herein that they beapplied for use in improving digital to analog conversion. Suchconversion from the digital domain to the analog domain may be performedwithin any of a variety of contexts including communication systems,storage devices, etc. Sometimes, a given device includes functionalityand/or circuitry therein for performing both conversion from the digitaldomain to the analog domain as well as conversion from the analog domainto the digital domain. For example, within a communication device suchas a transceiver, generation of signals for transmission into one ormore communication channels may be associated with digital to analogconversion, and processing of signals received from one or morecommunication channels may be associated with analog to digitalconversion.

Aliased harmonic reduction, improved linearity, distortion cancellation,reduced skirt spectral skirts, and reduced spurious emissions inaccordance with the various principles and aspects presented herein, maybe performed for use by one or more digital to analog converters (DACs)within any of a variety of communication systems and/or applications.Such processing techniques, architectures, and/or approaches presentedherein can be employed within a wide variety of communication systems,some types of which are described below.

Generally speaking, the goal of digital communications systems is totransmit digital data from one location, or subsystem, to another eithererror free or with an acceptably low error rate. In accordance with suchdigital communication systems, digital information is oftentimestransmitted from one communication device to at least one other. Withina transmitting communication device, digital information typicallyundergoes various processing to generate an analog signal suitable forlaunching into a communication channel. At the other end of thecommunication channel, a receiving communication device processes thereceived analog signal, which may have undergone some degradation orreduction in signal fidelity, in accordance with making estimates of theoriginal digital information that underwent processing within thetransmitting communication device. One of the processes performed withrespect to the received analog signal is analog to digital conversion.

As shown in FIG. 1, data may be transmitted over a variety ofcommunications channels in a wide variety of communication systems:magnetic media, wired, wireless, fiber, copper, and other types of mediaas well.

FIG. 1 and FIG. 2 are diagrams illustrate various embodiments ofcommunication systems, respectively.

Referring to FIG. 1, this embodiment of a communication system is acommunication channel 199 that communicatively couples a communicationdevice 110 (including a transmitter 112 having an encoder 114 andincluding a receiver 116 having a decoder 118) situated at one end ofthe communication channel 199 to another communication device 120(including a transmitter 126 having an encoder 128 and including areceiver 122 having a decoder 124) at the other end of the communicationchannel 199. In some embodiments, either of the communication devices110 and 120 may only include a transmitter or a receiver. There areseveral different types of media by which the communication channel 199may be implemented (e.g., a satellite communication channel 130 usingsatellite dishes 132 and 134, a wireless communication channel 140 usingtowers 142 and 144 and/or local antennae 152 and 154, a wiredcommunication channel 150, and/or a fiber-optic communication channel160 using electrical to optical (E/O) interface 162 and optical toelectrical (0/E) interface 164)). In addition, more than one type ofmedia may be implemented and interfaced together thereby forming thecommunication channel 199.

Either one or both of the communication device 110 and the communicationdevice 120 can include a hard disk drive (HDD) (or be coupled to a HDD).For example, the communication device 110 can include a HDD 110 a, andthe communication device 120 can include a HDD 120 a.

In some instances, to reduce transmission errors that may undesirably beincurred within a communication system, error correction and channelcoding schemes are often employed. Generally, these error correction andchannel coding schemes involve the use of an encoder at the transmitterand a decoder at the receiver. Clearly, a given communication device mayinclude both an encoder and a decoder to effectuate bi-directionalcommunication with one or more other communication devices; in otherembodiments, a given communication device includes only encodingfunctionality (e.g., a transmitter type communication device) or onlydecoding functionality (e.g., a receiver type communication device).

Any of the various types of imbalance and distortion cancellationdescribed herein, and their equivalents, can be employed within any suchdesired communication system (e.g., including those variations describedwith respect to FIG. 1), any information storage device (e.g., hard diskdrives (HDDs), network information storage devices and/or servers, etc.)or any application in which information encoding and/or decoding isdesired.

Referring to the communication system of FIG. 2, at a transmitting endof a communication channel 299, information bits 201 are provided to atransmitter 297 that is operable to perform encoding of theseinformation bits 201 using an encoder and symbol mapper 220 (which maybe viewed as being distinct functional blocks 222 and 224, respectively)thereby generating a sequence of discrete-valued modulation symbols 203that is provided to a transmit driver 230 that uses a DAC (Digital toAnalog Converter) 232 to generate a continuous-time transmit signal 204and a transmit (TX) filter 234 to generate a filtered, continuous-timetransmit signal 205 that substantially comports with the communicationchannel 299.

At a receiving end of the communication channel 299, continuous-timereceive signal 206 is provided to an AFE (Analog Front End) 260 thatincludes an automatic gain control (AGC) circuit or module 261, areceive (RX) filter 262 (that generates a filtered, continuous-timereceive signal 207) and one or more ADCs (Analog to Digital Converters)264 (that generates discrete-time receive signals 208). The ADC(s) 264may be viewed as incorporating imbalance and distortioncancellation/compensation functionality in accordance with theprinciples and/or aspects of the invention presented herein; suchfunctionality may be directed to embodiments including two or more ADCs.Greater details are provided herein regarding various means by whichsuch imbalance and distortion cancellation may be effectuated. A metricgenerator 270 calculates metrics 209 (e.g., on either a symbol and/orbit basis) that are employed by a decoder 280 to make best estimates ofthe discrete-valued modulation symbols and information bits encodedtherein 210. The decoder 280 may be a forward error correction (FEC)decoder employing any of a variety of error correction codes (ECCs).

Within each of the transmitter 297 and the receiver 298, any desiredintegration of various components, blocks, functional blocks,circuitries, etc. therein may be implemented. For example, this diagramshows a processing module 280a as including the encoder and symbolmapper 220 and all associated, corresponding components therein, and aprocessing module 280 is shown as including the metric generator 270 andthe decoder 280 and all associated, corresponding components therein.Such processing modules 280 a and 280 b may be respective integratedcircuits. Of course, other boundaries and groupings may alternatively beperformed without departing from the scope and spirit of the invention.For example, all components within the transmitter 297 may be includedwithin a first processing module or integrated circuit, and allcomponents within the receiver 298 may be included within a secondprocessing module or integrated circuit. Alternatively, any othercombination of components within each of the transmitter 297 and thereceiver 298 may be made in other embodiments.

As the reader will understand, various aspects and principles of theinvention are operative to ensure proper performance in accordance withconversion of one or more signals from the digital domain to the analogdomain. For example, such deleterious effects as clipping, aliasing,higher-order harmonics, etc. may be mitigated within one or more DACsemployed to perform conversion of one or more signals from the digitaldomain to the analog domain.

The processing of signals within either of the previous embodiments maybe implemented to include various aspects and/or embodiments of theinvention therein (e.g., any such embodiment that includes conversion ofone or more signals from the digital domain to the analog domain, suchas by one or more DACs, etc.). In addition, several of the followingFigures describe other and particular embodiments (some in more detail)that may be used to support the devices, systems, functionality and/ormethods that may be implemented in accordance with certain aspectsand/or embodiments of the invention.

3 illustrates an embodiment 300 of digital to analog conversion. Inaccordance with conversion of signals from the digital domain to theanalog domain, such conversion processing may be effectuated using adigital to analog converter (DAC). Data (e.g., digital, codewords, etc.)is provided to a DAC from which an analog signal is output. Oftentimes,the digital signal is composed of symbol labels, codewords, etc. thatrespectively are mapped to a corresponding voltage. For example,depending upon the particular value of a codeword that is provided to aDAC, a corresponding voltage is output from that DAC.

Referring to the lower left-hand side of the diagram, it can be seenthat as different respective codewords are provided to a DAC,corresponding output voltages are provided from that DAC. Oftentimes,such a DAC performs the appropriate processing to ensure that the analogsignal is in fact a continuous time signal. Again, as mentionedelsewhere herein, such terminology as analog signal, continuous timesignal, etc. may be used interchangeably.

A DAC will oftentimes have a particular linear operating range.Referring to the right-hand side of the diagram, it can be seen that thelinear operating range of a DAC may be viewed as extending between apositive saturation voltage and a negative saturation voltage. When acodeword is provided to the DAC that corresponds to a voltage that isbeyond this linear operating range, the actual output voltage from theDAC will be clipped back to the respective positive saturation voltageor the negative saturation voltage.

It is noted that such operation, such as saturation or overloading ofthe DAC, can result in a number of deleterious effects includingnonlinear distortion, clipping, aliasing, generation of intermodulationproducts, higher-order harmonics being aliased downward in frequency,etc.

Herein, a variety of different approaches are presented to deal with,minimize, reduce, or eliminate such deleterious effects. In variousembodiments, distortion synthesis is performed for use in improvingdigital to analog conversion. In some instances, the distortionsynthesis is particularly targeted in dealing with relatively lowfrequency and/or narrow bandwidth spurious emissions that may begenerated in accordance with imperfect digital to analog conversion.Sometimes, a second DAC is particularly employed to deal with suchrelatively low-frequency and/or narrow bandwidth spurious emissions.

In even other instances, the distortion synthesis is particularlytargeted in dealing with improving transition band and/or stopbandperformance. Generally speaking, such distortion synthesis is directedtowards reducing energy above a Nyquist folding frequency. By providingbetter stopband attenuation, much more efficient network operation maybe achieved. Oftentimes, a second DAC is employed to reduce the energyin the transition band and/or at and beyond the onset of the stopband.

In yet other instances, the distortion synthesis is particularlytargeted in dealing with devices that perform digital to analogconversion such that the folding frequency is relatively much wider thanthe transmitter bandwidth in a given operational mode. In certain suchembodiments, the distortion synthesis may be understood as applying anAM-AM and AM-PM characteristic corresponding to an estimate of thecharacteristic memory-less nonlinearity that the signal path issubjected to. Other nonlinear synthesis models apply in other certainapplications. In some applications, different nonlinear distortion terms(e.g., x², x³, etc.) are synthesized. From certain perspectives and incertain situations, distortion synthesis may be viewed as beingsubstantially different than pre-distortion. Such characteristics may beadapted based upon feedback corresponding to various respective powermeasurements as well as by adapting coefficients operating upon thesynthesized and filtered distortion terms. Within various embodimentsand/or diagrams herein, such power measurements may be effectuated usingan integrated or implemented one or more power measurement functionalblocks, circuitries, and/or modules, etc. Alternatively, such powermeasurements may be effectuated using an externally located powermeasurement functional blocks, circuitries, and/or modules, etc. (e.g.,a commercially available spectrum analyzer having access to such nodes,points, etc. within a device via one or more input and/or output ports).A designer is provided a wide variety of options by which such powermeasurements may be effectuated in accordance with various aspects,embodiments, and/or their equivalents of the invention.

It is noted that such improvements as may be effectuated for digital toanalog conversion of signals may be implemented within any of a varietyof devices. The context of communication systems, a communication devicewill oftentimes include at least one DAC. Digital signals are convertedinto analog signals in accordance with generating a signal that iscompliant with a communication channel with which such a communicationdevice may interact. Such types of communication devices includetransceivers, transmitters, etc. and generally any type of communicationdevice that will perform digital to analog conversion of signalstherein. In addition, other types of devices may also include inaccordance with various aspects, and their equivalents, of the variousmeans, functionalities, architectures, etc. as presented herein foreffectuating digital to analog conversion of signals. That is to say,certain types of devices that are not necessarily communication devicesmay nonetheless performed digital to analog conversion in accordancewith their respective operation. Any such device implemented to performdigital to analog conversion can employ such functionality as describedherein.

Within many of the various embodiments and/or diagrams presented herein,it is noted that certain additional components, functional blocks,circuitries, etc. may also be included without departing from the scopeand spirit of the invention. For example, certain embodiments and/ordiagrams illustrate respective subsets of different components,functional blocks, circuitries, etc. that can operate in conjunction andcooperatively with one another. Moreover, it is noted that alternativeembodiments may be viewed as being respective subsets of the components,functional blocks, circuitries, etc. included within a pictoriallyillustrated embodiment and/or diagram (e.g., in accordance with variousaspects, and their equivalents, of the invention may be found within asubset of the components, functional blocks, circuitries, etc. includedwithin a given diagram).

FIG. 4 illustrates an embodiment 400 of distortion synthesis forimproving digital to analog conversion. As can be seen with respect tothis diagram, data is provided to a modulator. Such a modulator may be asingle channel modulator or a multichannel modulator. That is to say,such a modulator may be implemented to generate a composite signalcorresponding to multiple channels such as in accordance with amultichannel modulator, or alternatively, such a modulator may beimplemented to generate a given signal corresponding to a singularchannel In some embodiments, the modulator contains an adaptable buffer,which in some applications is used to compensate for delays inherent innarrowband filtering in the synthesized signal path.

For example, within certain application contexts, a modulator may beimplemented for generating a large number of downstream quadratureamplitude modulation (QAM) channels on a singular radio frequency (RF)port. In one particular application, such as in accordance withcommunications compliant with the Data Over Cable Service InterfaceSpecification (DOCSIS), for particularly in the case of communicationscompliant in accordance with the DOCSIS Radio Frequency Interface (DRFI)specification, a modulator may be implemented for generating a largenumber of downstream QAM channels on a single RF port, and thespecification also places stringent emissions requirements for thegenerated signal. In some embodiments, such a modulator may be viewed asbeing a “dense modulator”, in that, a number of downstream channels mustbe able to be provided from a singular modulator. It is also noted thatsuch a dense modulator must be capable of generating as few as one or arelatively small number of QAM channels. The DRFI spurious emissionsrequirements for such applications are beyond what the currentstate-of-the-art can provide, namely, with respect to the combination ofa dense modulator and digital to analog converter (DAC). Generallyspeaking, many DACs that provide for an acceptable level of complexitydo not meet the aliased second (2nd) harmonic performance requirementsnecessary for emissions compliance, and as such, are not amenable forapplication in accordance with DRFI modulator applications. Upstreammodulators and transmitters within cable modems (CMs) are also subjectto spurious emissions requirements, among other fidelity requirements,in the DOCSIS 3.0 PHY specification, and meeting these requirements isalways balanced with the challenge of meeting high transmission powerand reducing complexity of the transmitter, including oftentimes a DACimplemented therein.

Referring again to the diagram, from the modulator, different respectivecodewords are provided to a synthesizer for generating one or moredistortion terms. In alternative embodiments, instead of providingcodewords directly from the modulator to the synthesizer, the signaloutput from the modulator is provided to the synthesizer for use by thesynthesizer in generating the one or more distortion terms. In evenother particular embodiments, some combination of codewords and thesignal output from the modulator are employed by the synthesizer for usein generating the one or more distortion terms. Alternatively,distortion terms may be sufficiently characterized and understood thatan algorithmic computation may be available and sufficient to compute(determine) the distortion terms from a current (or soon to be employed)operational mode (e.g., number of active transmitting channels and theircenter frequencies, symbol rates, power levels, etc.).

The one or more distortion terms may be predetermined. For example,depending upon a priori knowledge, experience, operational history, etc.of a given device, such distortion terms may be determined. For example,such distortion terms may be calculated beforehand and off-line andstored in a memory (e.g., a lookup table). That is to say, certainimplementations may be sufficiently characterized and sufficiently knownthat the distortion terms may be predetermined.

In other embodiments, such distortion terms are determined in real-time.For example, as may also be seen with respect to other embodiments,certain frequency selective measurements may be made and the resultsthere from may be used to select one or more distortion terms.

The one or more distortion terms are then combined with the signaloutput from the modulator thereby generating a modified signal that isprovided to the DAC. It is of course noted that, depending upon theparticular implementation, the one or more distortion terms output fromthe synthesizer may be negative in value such that they actually areadded to the signal output from the modulator. In other particularimplementations, the one or more distortion terms output from thesynthesizer may be positive value such that they are actually subtractedfrom the signal output from the modulator. The reader will understandthat different and various implementations may be made for effectuatingthe removal of such distortion from the signal output from themodulator. Pictorially, many of the embodiments depicted hereinindicated that one or more distortion terms are subtracted from thesignal output from the modulator. Again, however, it is noted thatdepending upon the sign convention employed for the one or moredistortion terms, those distortion terms may be added to or subtractedfrom the signal output from the modulator for effectuating the removalof distortion from that signal output from the modulator.

The modified signal, having reduced and/or eliminated distortion, isthen provided to the DAC from which an analog signal is output. Byeffectively eliminating distortion from the signal output from themodulator before it is provided to the DAC, spurious emissions from adevice performing such digital analog conversion may be significantlyreduced. In other applications, the modified signal prior to the DACcontains the inverse of distortion terms which have yet to be generatedin the processing flow, since they are generated within the DAC and/orthe following analog components (e.g., from nonlinear operationdominated by the relative high power and/or high power spectral densitycomponents comprising the signal). After the generation of thedistortion in the DAC and/or the following analog components, the newlygenerated distortion is reduced and/or eliminated by the presence of therelatively small power synthesized distortion injected prior to the DAC.By effectively creating the additive inverse of the distortionintroduced at and/or following the DAC, and injecting it before the DAC,distortion is substantially eliminated from the signal output followingthe DAC, and spurious emissions from a device performing such digitalanalog conversion may be significantly reduced.

It is noted that such an analog signal output from the DAC may beprovided to any of a number of different modules, circuitries, etc.within a communication device in accordance with generating a signal tobe launched into a communication channel For example, such subsequentmodules, circuitries, etc. may include a local oscillator, a mixer foreffectuating frequency conversion such as up conversion, etc.

Considering an exemplary embodiment, consider a DAC operating with aclocking frequency of 2.3 Gsps (Giga-samples per second) and having afolding frequency of 1.15 GHz. In this illustrative embodiment, thereare two 6 MHz wide channels centered at 850 MHz and at 900 MHz,respectively. The second harmonics are at 1700 MHz and 1800 MHz,respectively, and some third order intermodulation products are at 800MHz and at 950 MHz, respectively. However, oftentimes the distortionproducts associated with a DAC are generated in a manner which resultsin their aliasing down in frequency to below the folding frequency. Inthis embodiment, the aliased second harmonics fall at 500 MHz and 600MHz, respectively. Knowing that there are only the two channels, andknowing their respective center frequencies (and other characteristicssuch as bandwidth, etc.), the frequency location of some intermodulationproducts (perhaps aliased, though not in this example) and the aliasedsecond order harmonics (or perhaps not aliased, but they are aliased inthis example), the second order nonlinearity can be applied to thecomplex baseband embodiment of each of the channels and up-converted andspectrally inverted (both via digital operations in one possibleembodiment as pictorially illustrated in FIG. 5 which is additionallydescribed below using dashed lines for the filter and/or up-converter)when applicable (noting that the aliased harmonics in this example arespectrally inverted since the aliasing is caused by the actual secondharmonics mixing with the clocking frequency from the low side, e.g.,the harmonics are at frequencies lower than the clocking frequency) tosynthesize the 2nd order distortion products of the two respectivechannels.

Filtering to isolate and/or separate the various 2^(nd) order distortionproducts (and/or aliased 2^(nd) order distortion products) may beapplied, and each separated and/or isolated component may be operatedwith a different gain and phase, and other filtering, prior to injectioninto the SOI path. Higher order distortion products, aliased andnon-aliased, are synthesized in the same fashion. For synthesizingintermodulation products of channels, the same complex baseband approachmay be applied, operating on the product of the complex basebands,and/or the exponentiation of one or each of the complex basebands andthen generating the product of them (for the higher orderintermodulation products). Another embodiment uses an upconvertedversion of at least one of the modulated channels, rather than complexbaseband, but repeating the same steps as just outlined. In thisembodiment, as in the other, adjustment of the frequency location ofeach synthesized distortion component is required, via a frequencytranslation, prior to injection into the SOI.

FIG. 5 illustrates an alternative embodiment 500 of distortion synthesisfor improving digital to analog conversion. This diagram has somesimilarities to the previous embodiment with at least one differencebeing that two different digital to analog converters are employed.These two digital analog converters may operate at the same clocking (orequivalently, conversion or sampling) frequency, or the second DAC mayoperate at a different frequency than the first DAC. Generally speaking,in the art, it is noted that the frequency or rate at which a DACoperates is oftentimes loosely referred to as the sampling frequency orsampling rate, even though a signal is not being sampled in accordancewith DAC operations, but a continuous time signal is instead beinggenerated based on digital information.

In this diagram, instead of combining the one or more distortion termswith the signal that is output from the modulator, a second DAC isoperative to generate an additional analog signal that is combined withthe analog signal output from the first DAC. It is noted that the analogsignal output from the second DAC is operative to reduce distortionwithin the analog signal output from the first DAC upon theircombination.

As can be seen, at least one difference between this diagram (FIG. 5)and the previous diagram (FIG. 4) is that the distortion is effectivelypresent in the signal generated by the first DAC within this diagram,after which it is reduced, while the distortion is effectively reducedat and/or before the DAC in the previous diagram. A designer is provideda great deal of latitude by which to implement the combination ofsignals to improve performance of spurious emission performance of adevice operative to perform digital to analog conversion. It is notedthat the second DAC may operate over a relatively narrower bandwidththan the first DAC, enabling a lower clocking rate for the second DAC incomparison with the first DAC. The output from the second DAC may beupconverted by analog means prior to combining with the output from thefirst DAC (as depicted using dotted or dashed lines in the diagram). Theoutput from the second DAC may be lowpass filtered or bandpass filteredbefore and/or after upconversion, if any, prior to combining with theoutput of the first DAC. It is noted that the output of the second DACmay be many orders of magnitude lower power than the output of the firstDAC, enabling reduction in complexity of this second DAC compared to thefirst DAC, especially if combined with lower clocking rate.

It is also noted that the power dissipation of operating the second DACmay be substantially lower than the power dissipation of operating thefirst DAC. Also, the peak voltage excursions of the second DAC may alsobe substantially lower than for the output of the first DAC, withassociated savings in complexity, including the number of bits requiredfor the digital codewords converted in the second DAC. Also, in somesituations, the combining of the second DAC output with the first DACoutput can involve insertion loss of the signal from the first DAC, butby employing an uneven combining ratio with more weight provided for theoutput of the first DAC, the insertion loss of the signal from the firstDAC is reduced at the expense of requiring higher power for the outputof the second DAC. It is also noted that the rate of occurrence of thepeak power in the second DAC (or in the signal added to the primarysignal, when the combining is prior to the DAC) is often low, occurringrelatively infrequently; as such, the average power of this synthesizedand adapted signal may be dominated by relatively few peak occurrences.Still, the second DAC often operates with substantially lower voltageexcursions than the first DAC, and it is beneficial in some embodimentsto heavily weight the output from the first DAC at the combiner, toreduce insertion loss on the first DAC output, and to then operate thesecond DAC at higher output levels corresponding to the reducedweighting this signal is provided in the combining.

FIG. 6 illustrates an embodiment 600 of distortion synthesis, includingadaptation thereof, for improving digital to analog conversion includingimproving spurious emission performance. As shown in this diagram, anadapter is operative to modify one or more distortion terms as may begenerated by a synthesizer. The adapter may be driven by one or morefrequency selective measurements such as may be provided from the analogdomain. For example, based upon processing of the analog signalgenerated by the DAC, and particularly based upon frequency selectivemeasurements of that analog signal or derivations thereof, the adapteris implemented selectively to modify any distortion terms may begenerated by the synthesizer.

As may be understood with respect to this diagram, the one or moredistortion terms as may be provided from the synthesizer need notnecessarily be only predetermined or fixed values, but they may bemodified and tailored particularly for a given application.

It is noted that such an adapter as may be implemented within thisdiagram as well as different adapters that may be implemented withinother diagrams and/or embodiments may be implemented to perform avariety of functions. For example, such an adapter may be implemented toperform adaptation of any one of filtering, gain, phase, delayadjustment, etc. That is to say, such an adapter may be implemented toperform modification of any one or more distortion terms provided fromthe synthesizer in accordance with a variety of different operations.

Within the embodiment of this diagram as well as within embodimentscorresponding to other diagrams herein, it is noted that the frequencyselective measurements provided to the adapter may be provided via oneor more components implemented within a common device. That is to say,such frequency selective measuring component may be implemented withinthe very same device including those components employed to effectuatesuch digital to analog conversion. Alternatively, such frequencyselective measurements may be provided by one or more componentsexternal to the device actually performing the digital to analogconversion. For example, with respect to an embodiment making frequencyselective power measurements, a spectrum analyzer may be implementedwithin the device or a communication there with. In some instances, ananalog to digital converter (ADC) may be implemented to sample theanalog signal output from the DAC thereby generating a digital signalcorresponding to that analog signal for subsequent processing andanalysis thereof. Generally speaking, any of a variety ofimplementations may be effectuated for providing at least one frequencyselective measurement for use by an adapter such as implemented withinthis or other embodiments.

Generally speaking, an active nonlinear distortion mitigation techniquemay be implemented by performing such adaptation of one or moredistortion terms provided from a synthesizer.

As described with respect to this diagram and other diagrams and/orembodiments herein, in accordance with performing such active distortioncancellation, a measurement of one or more critical fidelitycharacteristics of the output signal (e.g., the analog signal outputfrom the DAC or a signal derived there from) is employed to guide theadaptive distortion cancellation as effectuated by the one or moredistortion terms provided from the synthesizer and adapted by theadapter. For example, such frequency selective measurements which may betaken in the analog domain are employed to drive the adaptation of theone or more distortion terms provided from the synthesizer.

In some embodiments, such adaptation of the one or more distortionterms, and/or respective coefficients associated therewith, may beperformed in accordance with performing dithering as an alternative toperforming a least mean square (LMS) algorithm. That is to say, such anarchitecture as presented herein that is operative to provide suchfrequency selective measurements may not necessarily provide a trueerror signal. That is to say, certain frequency selective measurements,such as frequency selective power measurements, are not directlyapplicable for use in accordance with the LMS algorithm. For example,the fact that such an architecture as presented herein does not providesuitable error signal that may be used in accordance with the LMSalgorithm, dithering may alternatively be performed that is driven byappropriate timing of the dithering and of the frequency selectivemeasurements. Techniques for converging adaptive tap coefficients as analternative to the LMS algorithm, e.g., gradient steepest descent, maybe employed. Isolating one tap at a time for adjustment, and/oremploying dithering algorithms for testing the result, and then moving,or retaining, the most recent tap coefficient value are among ditheringalgorithms which may be employed in applications such as this (e.g.,with respect to certain U.S. utility patent applications, U.S. patents,and/or references incorporated by reference above as identified by 4,4.1, 5, and 5.1).

It is also noted that there may be certain difficulty in observing andmeasuring one or more fidelity components which are to be optimized.This may be caused by a number of reasons including the oftentimesdifficult requirement of achieving an acceptably high transmit power.Also, the fidelity requirement, such as the unwanted distortion terms,are oftentimes specified to be at extremely low levels compared to thetransmit power of the communication device. This relatively largedifference between the transmit power and the signal level at whichmeasurements need to be made can be challenging. For example, themeasured signal of interest may span a relatively large dynamic rangeincluding being very strong and also falling near the measurement noisefloor (e.g., being relatively very small). Moreover, differentapplications will require different amounts of distortion which may beallowed at various frequencies.

It is again noted that the synthesis of the one or more distortion termscan be implemented in any of a variety of ways. One implementationcorresponds to mitigating the second-order harmonic distortions thatalias down in frequency (especially below the lowest signal frequencywhere requirements can be the most challenging, such as in DRFI), andalso given the consideration that the DACs with acceptably lowcomplexity have the most difficulty meeting the requirements when thereare relatively few active channels, an approach where each pair ofactive channels is used to generate the corresponding second orderdistortion product (aliased as may be done by the DAC) may be viewed ashaving relatively limited complexity. As the number of active channelsis increased, such an approach may scale more than linearly incomplexity, but in certain cases, mitigation may no longer be necessary.For application to devices with relatively lower sampling rates in theprimary DAC (e.g., the DAC implemented along the signal of interestpath) using the full RF signal (or some intermediate version beyondbaseband) for synthesis of the one or more distortion terms may be moreacceptable.

FIG. 7 illustrates an alternative embodiment 700 of distortionsynthesis, including adaptation thereof, for improving digital to analogconversion including improving spurious emission performance. As can beseen when comparing this diagram to the previous diagram, two separateDACs, which may operate at the same or different frequencies, areimplemented such that one or more distortion terms as may be providedfrom a synthesizer, and which may be adapted by an adapter [whoseoperation may be driven by one or more frequency selective measurements]are employed by a second DAC to generate a second analog signal that iscombined with a first analog signal output from the first DAC.

Again, designers are provided a great deal of latitude by which toimplement the combination of signals to improve performance of spuriousemissions in accordance with performing digital to analog conversion.This diagram illustrates adaptation of one or more distortion terms inconjunction with distortion reduction being performed by combination ofsignals within the analog domain. That is to say, the distortion of thefirst analog signal output from the first DAC is effectuated viacombination with a second analog signal output from the second DAC thatcorresponds to the one or more distortion terms provided by thesynthesizer, which may have undergone adaptation in accordance with oneor more frequency selective measurements such as may be performed withinthe analog domain.

FIG. 8 and FIG. 9 illustrate other alternative embodiments 800 and 900,respectively, of distortion synthesis, including adaptation thereof, forimproving digital to analog conversion including improving spuriousemission performance.

Referring to embodiment 800 of FIG. 8, as can be seen with respect tothis diagram, an adapter is implemented to modify one or more distortionterms as may be provided from a synthesizer based upon control and/orinformation provided from one or more other components. In this diagram,an amplifier and/or filter may be implemented after the DAC in theanalog domain to perform various processing of the analog signal outputfrom the DAC. All embodiments need not necessarily include such anamplifier and/or filter. A coupler is implemented to provide an analogsignal representative of the analog signal to be provided down theanalog domain processing chain (e.g., as the SOI). Such a coupler may bea tap coupler having some specified operational parameter such astapping a signal in accordance with a certain power ratio (e.g., 20 dB).The signal provided from the coupler is provided to one or more filters.A singular filter having frequency selective capability may be employed.In such an embodiment, a frequency selective filter is operative tosweep among a number of different frequencies thereby selectivelyoutputting particular portions of the signal provided via the coupler.As may be understood, at any particular time, a certain spectralcomponent of the signal provided from the coupler may be output fromsuch a frequency selective filter.

Alternatively, a number of filters may be implemented such that eachrespective filter has a corresponding tuning characteristic. In such anembodiment, each of these respective filters is operative to output aparticular spectral component of the signal provided from the coupler.Depending upon which output is selected from which of the number offilters, and the desired spectral component of the signal provided fromthe coupler may be output from such a filter bank.

One or more power detectors is/are implemented to make powermeasurements corresponding to the outputs from the one or more filters.Somewhat analogous to various embodiments by which one or more filtersmay be implemented, a singular power detector may be implemented tomeasure power provided from a singular frequency selective filter, suchthat different power measurements made at different times correspondrespectively to different frequency spectral component of the signalprovided from the coupler via such a frequency selective filter.Alternatively, a number of power detectors may be implemented in anembodiment including a number of filters such that each respective powerdetector is implemented to measure power of a signal provided from arespective one of the filters. That is to say, such an embodiment maycorrespond to a one-to-one relationship between the number of filtersand the number of power detectors such that each power detectorcorresponds to one filter, and vice versa. In another embodiment, analternative implementation and/or equivalent of a tunable filter may beemployed using an adjustable local oscillator tone and a mixer, or evena two mixer approach such as heterodyne.

Regardless of the particular implementation of one or more filtersand/or one or more power detectors, such respective frequency selectivepower measurements are provided to a controller. For example, acontroller is implemented to coordinate operation of the variousrespective components within such a device. For example, such acontroller is operative to receive such frequency selective powermeasurements and to direct the operation of the synthesizer and theadapter based thereon. Also, the controller is operative to direct theoperation of the one or more filters and the one or more power detectorsas well.

As can be seen with respect to this diagram, adaptation as may beperformed by the adapter, and particularly as driven by the controller,is effectuated based upon frequency selective measurements correspondingto an analog signal generated by the DAC. In this diagram, suchfrequency selective measurements are made within the analog domain andprovided to a controller for driving adaptation within the digitaldomain. It is noted that such a controller may include a combination ofdigital and analog components therein for effectuating interactionbetween the respective analog and digital domains.

Referring to embodiment 900 of FIG. 9, as can be seen with respect tothis diagram in comparison to the previous diagram, two separate DACs(which may operate at the same or different frequencies) are employedsuch that distortion is reduced from the analog signal output from thefirst DAC by combination of another analog signal output from the secondDAC. As can be seen within this diagram as well as other diagrams, oneor more filters and/or one or more of converters may optionally beimplemented to process the signal by second DAC. Generally speaking,within this embodiment 900 and within other diagrams and/or embodiments,certain modules, functional blocks, circuitries, etc. may optionally beincluded within alternative embodiments (e.g., sometimes pictoriallyillustrated by dotted or dashed lines). Again, as described with respectto multiple other embodiments herein, reduction of distortion may beeffectuated within the digital domain via modification of a signal thatis provided to a DAC, or reduction of distortion may be effectuatedwithin the analog domain via modification of the signal output from theDAC.

While many of the previous diagrams and embodiments are directed towardsreducing or eliminating the deleterious effects of spurious emissions asmay be encountered in accordance with digital analog conversion, certainof the subsequent diagrams and embodiments deal respectively withimproving transition band performance and stopband performancecorresponding to digital to analog conversion. Also, certain subsequentembodiments are directed towards providing for additional skirt and/orspectral mask performance in accordance with such digital to analogconversion.

FIG. 10 illustrates an embodiment 1000 of distortion synthesis forimproving digital to analog conversion including improving transitionband and/or stopband performance. As can be seen with respect to thisdiagram, two separate DACs (which may operate at the same or differentfrequencies) are employed such that one or more distortion terms asprovided by a synthesizer are used to generate an additional analogsignal output from the second DAC. Along the processing chain outputfrom the first DAC, an amplifier may be implemented between the outputof the first DAC and one or more stopband filters. In addition, anup-converter may be implemented with respect to the output of the secondDAC to perform certain operations such as up frequency conversion (e.g.,such as in accordance with frequency up conversion as particularlyillustrated). Of course, certain embodiments need not include suchfrequency conversion functionality for processing the analog signaloutput from the second DAC.

Sometimes, a digital signal that is provided to a DAC for conversion toan analog signal has frequency characteristics corresponding to arelatively flat frequency response up to some particular frequency,f_(u), such that this particular frequency is below the Nyquist foldingfrequency (e.g., f_(s)/2) associated with the sampling frequency (e.g.,f_(s)) by which the DAC operates. That is to say, assuming that thefrequency at which the DAC operates is f_(s), then the relatively flatfrequency response of the digital signal extends up to f_(u) such thatf_(u)<f_(s)/2. Oftentimes, there is another frequency, f_(sb), which maybe higher than the Nyquist folding frequency, f_(sb)>f_(s)/2, which isthe lower frequency of a stopband, or may be at or below the Nyquistfolding frequency.

For certain applications, which may include being compliant withincertain requirements related to emissions and/or noise immunityrequirements, the power spectral density or some other characteristicassociated with a measure of spurious emissions within a communicationdevice (e.g., such as taken via a measurement from at least onecomponent following the DAC, which may be a measurement taken at theoutput of a transmitter communication device) may be required to haveattenuation below a given threshold at frequencies greater than thisother frequency, f_(sb). For example, certain applications require acommunication device to operate in accordance with a certain degree ofelectromagnetic compatibility, such that emissions and/or noise immunityrequirements of the device must be below a particular threshold. As canbe seen, the frequencies between the upper edge of the signal passband(e.g., f_(u)) and the lower edge of the stopband (e.g., f_(sb)) may beviewed as constituting a transition band. Employing a digital filter canimprove the performance in the transition band, such as by providing formore attenuation. However, the inclusion of such a digital filter canincrease complexity and may sometimes unfortunately introduce filteringdistortion (e.g., by providing a non-flat amplitude and group delayvariation (GDV)) to the signal and the passband.

Alternatively, one or more stopband filters may be implementedsubsequent to the DAC, such as depicted with respect to this diagram. Insome instances, depending on how close are the respective frequenciescorresponding to the upper edge of the signal passband (e.g., f_(u)) andthe lower edge of the stopband (e.g., f_(sb)), as well as the Nyquistfolding frequency, f_(s)/2, such a stopband filter as implemented withinthe analog domain may unfortunately introduce insertion loss (e.g., byreducing power from the DAC output) and may also add additionalamplitude and GDV filtering distortion.

A second DAC is implemented such that the energy between variousrespective frequencies can be reduced (e.g., (1) the energy between theupper edge of the signal passband, f_(u), and the Nyquist foldingfrequency, f_(s)/2, (2) the energy from the Nyquist folding frequency,f_(s)/2, to the lower edge of the stopband, f_(sb), as well as (3) theenergy within some range higher than the lower edge of the stopband,f_(sb), [between f_(sb) some f>f_(sb)]). That is to say, with suchinterference distortion cancellation techniques in accordance with thevarious approaches presented herein, and their equivalents, the energywithin certain particular frequency ranges can be reduced. Suchimplementation may be implemented using digital and/or analog filters asalso referred to above. That is to say, such interference distortioncancellation techniques may be employed in combination with orseparately from such digital and/or analog filters.

The additional reduction of signal energy in the transition band mayoperate to relax the requirements on any such implemented digital and/oranalog filters. Such a relaxation can enable the achievement of muchmore narrow transition bands and/or substantially less filteringdistortion in the passband and/or much more stopband attenuation. As thereader will understand, such an implementation may reduce the complexityof a given device while allowing for better stopband attenuation andsmaller transition bands. By providing for better stopband attenuation,much more efficient network operation may be achieved, such as inaccordance with a communication system application, in that, acommunication device will still introduce relatively less noise intoadjacent frequency bands during transmission of signals. By providingfor operation of relatively smaller transition bands, the overallnetwork efficiency may be increased by allowing for greater use of thespectrum. As may be understood, by ensuring relatively more narrowtransition bands, more frequency spectra is available for use for othercommunications. It is also noted that the use of such relatively smallertransition bands may further reduce implementation complexity, inaddition to that which is referenced above, by allowing for the use ofrelatively lower sampling rates within a DAC. For example, the samplingrate of the DAC is oftentimes increased to provide for more oversamplingin response to the inherent limitations of digital and/or analog filtersin supporting the attenuation needed at the lower edge of the stopband,f_(sb), within allowed or acceptable amount of filter distortion belowthe upper edge of the signal passband, f_(u).

FIG. 11 illustrates an embodiment 1100 of distortion synthesis,including adaptation thereof, for improving digital to analog conversionincluding improving transition band and/or stopband performance. As canbe seen with respect to this diagram, adaptation may be performed withrespect to one or more distortion terms provided by the synthesizer foruse by the second DAC in generating the second analog signal. As mayalso be understood with respect to other diagrams and embodimentsdescribed herein, such adaptation may be made with respect to frequencyselective measurements including those taken within the analog domainand related to the analog signal generated by the first DAC or signalsgenerated or derived therefrom.

FIG. 12 illustrates an alternative embodiment 1200 of distortionsynthesis, including adaptation thereof, for improving digital to analogconversion including improving transition band and/or stopbandperformance.

As can be seen with respect to this diagram, a coupler, one or morefilters (e.g., which may have frequency selective capability), one ormore power detectors, and a controller are implemented to direct theoperation of various components including that of the adapter. Generallyspeaking, an adapter is implemented to modify one or more distortionterms as may be provided from a synthesizer based upon control and/orinformation provided from one or more other components. In this diagram,an amplifier may be implemented after the first DAC in the analogdomain, after the first DAC and before the one or more stopband filters,to perform various processing of the analog signal output from the firstDAC. All embodiments need not necessarily include such an amplifier.

A coupler is implemented to provide an analog signal representative ofthe analog signal to be provided down the analog domain processingchain. As described also with respect to other embodiments herein, sucha coupler may be a tap coupler having some specified operationalparameter such as tapping a signal in accordance with a certain powerratio (e.g., 20 dB). The signal provided from the coupler is provided toone or more filters. A four port device could combine the combiningfunction and the coupling function adjacent to each other in the figure.A singular filter having frequency selective capability may be employed.In such an embodiment, a frequency selective filter is operative tosweep among a number of different frequencies thereby selectivelyoutputting particular portions of the signal provided via the coupler.As may be understood, at any particular time, a certain spectralcomponent of the signal provided from the coupler may be output fromsuch a frequency selective filter.

Alternatively, a number of filters may be implemented such that eachrespective filter has a corresponding tuning characteristic. In such anembodiment, each of these respective filters is operative to output aparticular spectral component of the signal provided from the coupler.Depending upon which output is selected from which of the number offilters, and the desired spectral component of the signal provided fromthe coupler may be output from such a filter bank.

One or more power detectors is/are implemented to make powermeasurements corresponding to the outputs from the one or more filters.Somewhat analogous to various embodiments by which one or more filtersmay be implemented, a singular power detector may be implemented tomeasure power provided from a singular frequency selective filter, suchthat different power measurements made at different times correspondrespectively to different frequency spectral component of the signalprovided from the coupler via such a frequency selective filter.Alternatively, a number of power detectors may be implemented in anembodiment including a number of filters such that each respective powerdetector is implemented to measure power of a signal provided from arespective one of the filters. That is to say, such an embodiment maycorrespond to a one-to-one relationship between the number of filtersand the number of power detectors such that each power detectorcorresponds to one filter, and vice versa.

Regardless of the particular implementation of one or more filtersand/or one or more power detectors, such respective frequency selectivepower measurements are provided to a controller. For example, acontroller is implemented to coordinate operation of the variousrespective components within such a device. For example, such acontroller is operative to receive such frequency selective powermeasurements and to direct the operation of the synthesizer and theadapter based thereon. Also, the controller is operative to direct theoperation of the one or more filters and the one or more power detectorsas well.

As can be seen with respect to this diagram, adaptation as may beperformed by the adapter, and particularly as driven by the controller,is effectuated based upon frequency selective measurements correspondingto an analog signal generated by the second DAC. In this diagram, suchfrequency selective measurements are made within the analog domain andprovided to a controller for driving adaptation within the digitaldomain. It is noted that such a controller may include a combination ofdigital and analog components therein for effectuating interactionbetween the respective analog and digital domains.

As may be understood with respect to this diagram, the use of one ormore stopband filters along the chain processing the analog signaloutput from the first DAC is operative to reduce energy within certainportions of the frequency spectrum. For example, such as describedfurther above, the energy within certain portions of the frequencyspectrum such as (1) the energy between the upper edge of the signalpassband, f_(u), and the Nyquist folding frequency, f_(s)/2, (2) theenergy from the Nyquist folding frequency, f_(s)/2, to the lower edge ofthe stopband, f_(sb), as well as (3) the energy within some range higherthan the lower edge of the stopband, f_(sb), [between f_(sb) somef>f_(sb)] may be reduced. Again, as also described elsewhere herein, byallowing for operation using relatively smaller transition bands,greater use of the available frequency spectrum may be achieved. Alsooverall network efficiency may be increased, at least in part, becauseof these relatively smaller transition bands. Moreover, relatively lowersampling rates may be employed by one or more DACs within such a device,and relatively lower implementation complexity may be achieved.

Certain of the following diagrams are directed towards improving skirtand/or spectral mask performance. For example, within a communicationdevice operative to perform transmission of one or more signals via oneor more communication links, certain applications require thecharacteristics of certain spectral masks to be in accordance withcertain constraints (e.g., meeting certain federal communicationscommission (FCC) regulations for wireless communications). Generallyspeaking, skirt and/or spectral mask performance may be implemented inaccordance with synthesizing one or more distortion terms and adding itto the signal of interest path in an effort to reduce the deleteriousdistortion effects therein. In certain embodiments, the one or moredistortion terms may be adapted (e.g., such as in accordance with theleast squared error (LSE) criterion), which may be based upon one ormore frequency selective measurements such as provided from the analogdomain.

In accordance with improving skirt and/or spectral mask performance, thesynthesis of one or more distortion terms may be implemented by applyingan AM-AM and AM-PM characteristic (e.g., an embodiment of which ispictorially illustrated with respect to FIG. 22). Such a characteristicmay be viewed as being an estimate of the characteristic memory-lessnonlinearity that the signal path is subjected to. In certain ofembodiments, this characteristic may be adapted based upon feedback(e.g., from frequency selective measurements). As may be understood, theone or more distortion terms, such as provided from a synthesizer, mayalso be adapted based upon such frequency selective measurements.Generally speaking, such applications are directed towards the instancein which the Nyquist folding frequency (e.g., f_(s)/2) is relativelymuch wider than the available bandwidth of interest. For example, withina communication system application, the Nyquist folding frequency (e.g.,f_(s)/2) may be viewed as being relatively much wider than the availabletransmission bandwidth by which communications may be made. Suchimprovement to the skirt and/or spectral mask performance may beachieved whether the skirt(s)/mask(s) are relatively much lower than theNyquist folding frequency (e.g., f_(s)/2) or whether one of theskirt(s)/mask(s) is within the transition band as described above withrespect to those embodiments directed towards reducing energy withincertain respective frequency ranges.

FIG. 13 illustrates an embodiment 1300 of distortion synthesis forimproving digital to analog conversion including improving skirt and/orspectral mask performance. Skirt and/or spectral mask requirements canbe applicable at frequencies below the Nyquist folding frequency. Assuch, part of the synthesized skirt and/or spurious emissions (withinthe spectral mask's associated frequencies) may be injected prior to theprimary (SOI) DAC to reduce the skirt and/or spurious emissions withinthe spectral mask, as when reducing aliased and non-aliased harmonicsand intermodulation distortion. Each skirt and spectral mask region maybe isolated and synthesized separately, though complete separation isnot necessary in all applications. As can be seen with respect to thisdiagram, a number of narrowband filters receive respective outputs fromthe synthesizer. In this diagram, the outputs from the respectivenarrowband filters are summed together and combined with the signaloutput from the modulator before being provided to the DAC. Eachrespective narrowband filter may operate in accordance with differentcharacteristics. For example, the respective narrowband filters may havedifferent respective frequency responses, attenuations, etc. such thatthe one or more distortion terms generated by the synthesizer arehandled differently.

FIG. 14 illustrates an alternative embodiment 1400 of distortionsynthesis for improving digital to analog conversion including improvingskirt and/or spectral mask performance. As can be seen with respect tothis diagram in comparison to the previous diagram, a first DAC and asecond DAC, which may operate at the same frequency or at differentfrequencies, receives the outputs from the respective narrowbandfilters, after having been summed together. As such, the analog signalgenerated from the second DAC corresponds to the combination of theoutputs from the respective narrowband filters. The analog signalprovided from the second DAC is combined with the analog signal outputfrom the first DAC.

Within this diagram and other embodiments that employ a second DAC forgenerating a second analog signal that is combined with the first analogsignal output from the first DAC, it is noted that the output power ofthe second DAC may be generally less than the output power of the firstDAC. In some instances, an amplifier is implemented to modify the analogsignal output from the first DAC; however, even within such instances,the output power of the second DAC may be less than the output power ofthe first DAC.

FIG. 15 illustrates an embodiment 1500 of distortion synthesis,including adaptation thereof, for improving digital to analog conversionincluding improving skirt and/or spectral mask performance. As can beseen with respect to this diagram, multiple respective outputs areprovided from the synthesizer to a number of narrowband filters. Eachrespective narrowband filter provides its output to a correspondingrespective adapter. The operation of the adapters may be performed basedupon one or more frequency selective measurements such as may be madewithin the analog domain. Different respective control signals may beprovided to each respective adapter such that each one operatesindependently from the other spectral band adaptive coefficients andbased upon the respective frequency selective measurements associatedwith the spectral band of the narrowband filter all along thatparticular processing path. That is to say, each respective adapter maybe adjusted independently with respect to the other adapters based uponfrequency selective measurements associated with its respective spectralband of influence.

In this particular diagram, the outputs from the respective adapters aresummed together and combined with the signal output from the modulatorbefore being provided to the DAC.

FIG. 16 illustrates an alternative embodiment 1600 of distortionsynthesis, including adaptation thereof, for improving digital to analogconversion including improving skirt and/or spectral mask performance.As can be seen with respect to this diagram in comparison to theprevious diagram, a coupler, one or more filters (e.g., which may havefrequency selective capability), one or more power detectors, and acontroller are implemented to direct the operation of various componentsincluding that of the respective adapters. For example, the operation ofthe respective adapters may be adjusted based on direction from thecontroller. In some instances, the controller is also operative todirect the operation of the respective narrowband filters. For example,the frequency responses, attenuations, etc. of the respective narrowbandfilters may be adjusted based upon direction from the controller.

The reader is referred to other diagrams and/or embodiments includedherein that described the operation of such couplers, one or morefilters (such as those being frequency selective), etc. such as isdescribed elsewhere herein.

FIGS. 17 and 18 illustrate other alternative embodiments 1700 and 1800,respectively, of distortion synthesis, including adaptation thereof, forimproving digital to analog conversion including improving skirt and/orspectral mask performance.

Referring to embodiment 1700 of FIG. 17, as can be seen with respect tothis diagram, the outputs from the multiple adapters are summed togetherand provided to a second DAC operative to generate a second analogsignal that is combined with the analog signal output from the firstDAC. It is noted that the respective adapters may operate based uponcertain frequency selective measurements such as may be provided fromthe analog domain.

Referring to embodiment 1800 of FIG. 18, as can be seen with respect tothis diagram, in comparison to the previous diagram, a coupler, one ormore filters (e.g., which may have frequency selective capability), oneor more power detectors, and a controller are implemented to direct theoperation of various components including that of the respectiveadapters. For example, the operation of the respective adapters may beadjusted based on direction from the controller. In some instances, thecontroller is also operative to direct the operation of the respectivenarrowband filters. For example, the frequency responses, attenuations,etc. of the respective narrowband filters may be adjusted based upondirection from the controller.

The reader is referred to other diagrams and/or embodiments includedherein that described the operation of such couplers, one or morefilters (such as those being frequency selective), etc. such as isdescribed elsewhere herein.

FIG. 19 illustrates an embodiment 1900 of distortion synthesis,including adaptation thereof and separately compensating for frequenciesabove and below, respectively, of a signal of interest, for improvingdigital to analog conversion including improving skirt and/or spectralmask performance. With respect to this diagram, three separate DACs areimplemented. A first DAC is implemented along the main processing line,in accordance with generating an analog signal from the codewordsprovided from the modulator. A second DAC is implemented to generate asecond analog signal based upon the summed outputs from a first subsetof the narrowband filters. This second DAC corresponds to those signalcomponents below a particular signal of interest (e.g., below aparticular frequency of interest, f_(int)).

Analogously, a third DAC is implemented to generate a third analogsignal based upon the second outputs from a second subset of thenarrowband filters. This third DAC corresponds to those signalcomponents above that particular signal of interest (e.g., abovef_(int)). The respective analog signals output from the second DAC andthe third DAC are combined, and that resulting combination is thencombined with the output from the first DAC.

Generally speaking, the narrowband filter synthesized outputs are summedtogether according to their respective spectral position in comparisonto that of the signal along the main processing path (e.g., the signalpath extending from the modulator to the first DAC). For example, therelatively high side frequency outputs are summed together, and therelatively low side frequency outputs are summed together. That is tosay, a first subset of the narrowband filters corresponds to therelatively high side frequency, and a second subset of the narrowbandfilters corresponds to the relatively low side frequency. As can be seenwith respect to the diagram, the two respective summed signals arepassed to their own respective DACs. It is noted that the second DAC andthe third DAC may operate at different frequencies than the first DAC.For example, the second DAC and the third DAC may operate at relativelylow lower rates than the first DAC. Also, various frequency conversion(e.g., up conversion), may be performed before or after summation withinthe different respective subsets, or alternatively after generation ofthe respective analog signals output from the second back in the thirdDAC.

As can be seen with respect to this diagram, an AM-AM and AM-PMcharacteristic is employed to model the one or more distortion terms(e.g., an embodiment of which is pictorially illustrated with respect toFIG. 22). That is to say, such an architecture may be viewed as modelingone or more channels in accordance with such a characteristic tosynthesize the one or more distortion terms.

FIG. 20 and FIG. 21 illustrate alternative embodiments 2000 and 2100,respectively, of distortion synthesis, including adaptation thereof andseparately compensating for frequencies above and below, respectively,of a signal of interest, for improving digital to analog conversionincluding improving skirt and/or spectral mask performance.

Referring to embodiment 2000 of FIG. 20, as may be seen with respect tothis diagram, three separate DACs are implemented as with respect to theprevious diagram. In this diagram, a first DAC is a political of mainprocessing line, and a second DAC and a third DAC are implemented withrespect to and corresponding to those signal components above and belowthe particular signal of interest (e.g., above and below f_(int)), and anumber of adapters are implemented such that the output from eachrespective narrowband filter is provided to a corresponding andrespective adapter.

As can be seen with respect to this diagram, multiple respective outputsare provided from the synthesizer to a number of narrowband filters.Each respective narrowband filter provides its output to a correspondingrespective adapter. The operation of the adapters may be performed basedupon one or more frequency selective measurements such as may be madewithin the analog domain. Different respective control signals may beprovided to each respective adapter such that each one operatesindependently from the other spectral band adaptive coefficients andbased upon the respective frequency selective measurements associatedwith the spectral band of the narrowband filter all along thatparticular processing path. That is to say, each respective adapter maybe adjusted independently with respect to the other adapters based uponfrequency selective measurements associated with its respective spectralband of influence.

In addition, it can be seen that the narrowband filters and adapters arepartitioned into at least two groups such that a first subset of thenarrowband filters and adapters correspond to those signal componentbelow a particular signal of interest (e.g., <f_(int)). A second subsetof the narrowband filters and adapters correspond to those signalcomplements above that particular signal of interest (e.g., >f_(int)).

In this particular diagram, within each respective subset of thenarrowband filters and adapters, the outputs from those adapters withinthat subset are summed together and combined before being provided tothat respective DAC (e.g., outputs from a first subset of the adaptersare summed together and provided to the second DAC, and outputs from asecond subset of the adapters are summed together and provided to thethird DAC). The respective analog signals output from the second DAC andthe third DAC are combined, and that resulting combination is thencombined with the output from the first DAC.

Referring to embodiment 2100 of FIG. 21, as can be seen with respect tothis diagram, in comparison to the previous diagram, a coupler, one ormore filters (e.g., which may have frequency selective capability), oneor more power detectors, and a controller are implemented to direct theoperation of various components including that of the respectiveadapters. For example, the operation of the respective adapters may beadjusted based on direction from the controller. In some instances, thecontroller is also operative to direct the operation of the respectivenarrowband filters. For example, the frequency responses, attenuations,etc. of the respective narrowband filters may be adjusted based upondirection from the controller.

The reader is referred to other diagrams and/or embodiments includedherein that described the operation of such couplers, one or morefilters (such as those being frequency selective), etc. such as isdescribed elsewhere herein.

In even another embodiment, after the coupler, the energy of the signalof interest passband may be reduced prior to the error power filteringand measurement operations such as performed using one or more filters,one or more power detectors, etc. This may be reduced by differencingthe signal that is coupled away from the signal of interest path priorto an amplifier that may be implemented within that path. Such a signalof interest picked off prior to such an amplifier may be amplified (yetto a relatively lower amount than would be employed by the actualtransmitter output) and delay adjusted adaptively to minimize the powerin the resulting combination. Such additional components can provide fora reduction of the signal of interest power when the measurements aremade for driving the adaptive distortion cancellation. Reducing thesignal of interest power in such an active, adaptive manner may be moredesirable than standalone filtering in terms of providing more accuratemeasurements within certain embodiments. For example, sense relativelylarge signal of interest power can be problematic to error powermeasurements, especially near error measurement bands, such a reductionof the signal of interest power may be desirable in such embodiments.

FIG. 22 illustrates an embodiment 2200 of amplitude modulation-amplitudemodulation (AM-AM) characteristics and AM-phase modulation (AM-PM)characteristics. As can be seen with respect to this diagram, therelationships between an input amplitude and output amplitude andintroduced phase are sometimes depicted with respect to AM-AM and AM-PMcharacteristics, especially for bandpass signals undergoing poweramplification to high levels of output power. For example, with respectto AM-AM characteristics, there is a relatively linear relationshipbetween input and output amplitude (e.g., relatively near the origin)until the input amplitude exceeds a given value after which the outputamplitude generally remains at a maximum value. For example, when theinput amplitude is relatively large, the output amplitude willcorrespondingly generally not exceed a maximum value.

As can be seen with respect to AM-PM characteristics, there is arelatively negative linear relationship between input amplitude andoutput phase (e.g., having a negative relatively linear slope), by whichan output phase negatively follows the input amplitude in accordancewith such a negative relationship. As can be seen, the relative slope ofthe curve increases as a function of an increased input amplitude,corresponding to increased delay as the amplitude is increased. Thereader is referred to the technical literature for additional materialinformation as may be understood with respect to AM-AM characteristicsand AM-PM characteristics.

Within certain situations, relatively good knowledge may be known withrespect to where a given signal of interest is located, and one or morefilters may be implemented in order to improve performance. For example,an anti-aliasing filter may be employed to assist in one or morefrequency selective measurements as may be employed within such systems(e.g., such as those including frequency selective power measurement ordetection). By appropriately implementing such one or more modules,functional blocks, circuitries, etc., appropriate signal processing maybe effectuated so that the dynamic range requirements associated withsuch measurements including frequency selective measurements may beeffectively reduced. For example, when there is at least some knowledgeof one or more harmonics, intermodulation products, etc. within a signalof interest, certain signal processing may be performed to ensure thatmore accurate measurements including frequency selective measurementsmay be made without necessarily stringent requirements for associatedmeasurement modules, functional blocks, circuitries, etc. and/orequipment. That is to say, by employing appropriate signal processing,relatively lower end and not strictly high-performance measurementmodules, functional blocks, circuitries, etc. and/or equipment may beused without deleteriously affecting overall performance.

For example, certain embodiments operate by employing a copy of thesignal of interest and processing that copy in accordance withappropriate signal processing for improving associated measurementsincluding frequency selective measurements (e.g., power management ordetection). Such appropriate signal processing facilitates improvementin such measurements, and can be used to drive or direct the steepestdescent and/or dithering operation which may be employed for calculatingone or more tap values (e.g., in accordance with tap convergenceprocessing) by reducing the dynamic range at the input of suchmeasurement modules, functional blocks, circuitries, etc. and/orequipment in accordance with such noise canceling techniques asdescribed herein. Generally speaking, improvement of such measurementsincluding frequency selective measurements (e.g., power management ordetection) may be achieved by reducing the dynamic range at the input ofsuch measurement modules, functional blocks, circuitries, etc. and/orequipment.

In addition, it is noted that various embodiments operate in accordancewith a steepest descent and/or dithering operation which is used tocalculate one or more values (e.g., one or more values as may becalculated by controller that may drive operation of an adapter, one ormore filters including frequency tunable filters, a synthesizer, one ormore power detectors, etc. as may be understood with respect to otherdiagrams and/or embodiments herein), and such steepest descent and/ordithering operation may also be employed for selecting or calculatingone or more variable gain and/or phase taps within a signal of interest(SOI) (noise) canceller. However, it is noted that more than onerespective steepest descent and/or dithering operation will not beperformed at the same time in most embodiments. Example, while asteepest descent and/or dithering operation may be performed withrespect to selecting or calculating one or more variable gain and/orphase taps within a signal of interest (SOI) (noise) canceller, suchsteepest descent and/or dithering operations as may be performed by acontroller should be at least temporarily stopped. Generally speaking,it may be undesirable to switch multiple variables at a given time, andany steepest descent and/or dithering operations as may be employed by acontroller should be decoupled from any steepest descent and/ordithering operation operative for selecting or calculating one or morevariable gain and/or phase taps within a signal of interest (SOI)(noise) canceller.

Considering an exemplary embodiment in which the average power of thesignal at the input to the up-converter may be 60 dBmV, and the power atthe stronger output of the coupler may be 59 dBmV, or 56 dBmV in each oftwo channels, while the power at the lower output of the coupler may be40 dBmV total. The spurious emission requirement in some 6 MHz bandwidthmay be −70 dBc compared to the power in one channel, or −14 dBmV. Thespurious emissions requirement referenced to the coupler output to thepower measurement function is −33 dBc. It is noted that the thermalnoise floor at room temperature is −57.5 dBmV. A measurement system withan effective 15 dB noise figure places the measurement system noisefloor (for a 6 MHz bandwidth measurement) at −42.5 dBmV, whichdesensitizes the measurement of an at-spec amount of spurious emissionsin this example by less than 0.5 dB. This is sufficiently accurate todrive a gradient or steepest descent and/or dithering operation forconverging taps (e.g., dithering), since the desensitization isrelatively small and still allows monotonicity, which is critical.

It is noted that 15 dB noise figure for the measurement system is arelatively relaxed requirement, even for the frequencies of application,compared to commercial test equipment. As such, it may be noted thatrelatively lower end modules, functional blocks, circuitries, etc. maybe employed within a given embodiment for effectuating such measurementsincluding frequency selective measurements in comparison to that whichmay be provided by commercial test equipment; alternatively, relativelylower end commercial test equipment may be employed.

It is noted that the presence of the strong signal of interest istypically problematic in such measurements, and filtering to reduce thesignal of interest prior to power measurement, and thus the dynamicrange of the power measurement equipment, is provided in the typicalembodiment. One embodiment uses filtering to attenuate the signal ofinterest frequencies compared to the spurious emissions frequenciesintended for measurement, and the filtering is followed by powerdetection or measurement (e.g., which may be effectuated using an analogto digital converter (ADC) with sufficient linearity, e.g., with thereduced signal of interest power compared to the spurious emissionsspecification limit)) to prevent degrading amounts of intermodulationdistortion (and/or harmonic distortion) which would unduly desensitizethe power measurement in the frequencies where the spurious emissionsrequirements are applicable.

Another embodiment uses noise canceling techniques to further reduce theenergy in the signal of interest frequencies, compared to the spuriousemissions specification limit, prior to power measurement in spuriousemissions specification frequencies. For example, as described elsewhereherein, if at least some information is known regarding the signal ofinterest frequencies, appropriate signal processing may be made inaccordance with such noise cancellation techniques to reduce the dynamicrange at an input of one or more modules, functional blocks,circuitries, etc. and/or test equipment implemented to performmeasurements including frequency selective measurements (e.g., powerdetection or measurement). Of course, care must be taken to avoidsignificant corruption of the measurement of the targeted spuriousemissions when reducing signal of interest energy, or else the steepestdescent and/or dithering algorithm will be potentially corrupted bymisleading measurements.

The noise canceling techniques can be operative with analog means, withone or more analog variable gain and/or phase “tap” (e.g., such as inaccordance with a signal of interest (SOI) (noise) canceller aspictorially illustrated within FIG. 23, FIG. 24, intricately five).Steepest descent and/or dithering techniques may be employed inaccordance with selecting or calculating such one or more variable gainand/or phase taps. It is noted that in one embodiment with noisecanceling techniques applied to the signal of interest in themeasurement path that substantial filtering to relatively attenuate thesignal of interest is not needed.

With respect to such steepest descent and/or dithering operations, suchoperations may be generally described as measuring performance based ona first coefficient, then taking a step in a given direction anddetermining whether or not performance improved or degraded. If theperformance improved, then a second coefficient (e.g., being the firstcoefficient modified by the step) is then employed, and the process isrepeated. Alternatively, if the performance degraded, then the firstcoefficient is still employed, and a step is taken in the oppositedirection and the process operates by determining whether or notperformance improved or degraded. If the performance improved in thissecond/opposite direction, then a third coefficient (e.g., being thefirst coefficient modified by the step taken in the second/oppositedirection) is then employed, and the process is repeated. When noimprovement is achieved when stepping from a given coefficient in eitherdirection, then the latest resultant coefficient is that which isselected or computed in accordance with the steepest descent and/ordithering operation. In accordance with selecting or computing a tapcoefficient, such tap coefficient steepest descent and/or ditheringprocessing may be applied (a) for minimizing power measurements for bothminimizing the distortion created by the transmitter and also (b) forminimizing the signal of interest energy which desensitizes thedistortion power measurement. While a general description of thesteepest descent and/or dithering operation is provided herein, furtherdetails are included within the U.S. Utility application Ser. No.10/879,673, entitled “System and Method for adjusting multiple controlloops using common criteria,” filed on Jun. 29, 2004, now issued as U.S.Pat. No. 7,961,823 B2 on Jun. 14, 2011, which has been incorporated byreference herein as indicated above. For example, in the referencedapplication/patent, the same error power measurement undergoesminimization and is used for driving both of the respective function's(a) and (b) (described above) taps. The reader is referred to referencedapplication/patent for additional details regarding gradient or steepestdescent and/or dithering operation.

However, as applied with in various embodiments and/or diagrams herein,the same or different respective functions (a) and (b) (described above)may be employed to minimize the same error power measurement and todrive both of the respective function's (a) and (b) (described above)taps' convergence. In addition, in one particular embodiment, the powermeasurement driving the minimization of the signal of interest energythat desensitizes the noise or distortion power measurement isimplemented such that it intentionally captures more of the signal ofinterest bandwidth than is captured in accordance with the measurementof noise or distortion power which is driving the minimization of thetransmitter distortion.

FIG. 23 illustrates an embodiment 2300 of distortion synthesis,including adaptation thereof, for improving noise power measurement asmay be operative to reduce dynamic range associated with powermeasurement or detection or other frequency selective measurementsemployed therein. As can be seen within this diagram, two differentrespective couplers are implemented before and after an amplifier and/orfilter along the signal path extending from the DAC. The first couplerprovides a signal reference input, and the second coupler provides asignal plus noise input to a SOI (noise) canceller. The output from theSOI (noise) canceller may subsequently undergo measurement includingfrequency selective measurements (e.g., power detection or measurementby one or more power detectors). As also described elsewhere herein,such appropriate signal processing is effectual to improve noisemeasurements by reducing the dynamic range at an input of one or moremodules, functional blocks, circuitries, etc. and/or test equipmentimplemented to make such measurements. In the instant embodiment 2300,by employing the SOI (noise) canceller, the dynamic range is effectivelyreduced at the input of the one or more power detectors therebyimproving noise power detection or measurement.

Considering one embodiment where an amplifier and/or filter followingthe DAC is generating most of the harmful distortion products, couplingsome of the signal of interest away from this point (e.g., using thefirst coupler implemented after the DAC and before the amplifier and/orfilter) and using this as the signal reference input to the noisecanceller (e.g., SOI (noise) canceller), the noise canceller willoperate to reduce the signal of interest power substantially into thepower measurement function without substantially impacting(desensitizing) the spurious emissions power measurement, owing to thesignal reference input to the noise canceller not containing thespurious energy added by the amplifier and/or filter.

FIG. 24 and FIG. 25 illustrate alternative embodiments 2400 and 2500,respectively, of distortion synthesis, including adaptation thereof, forimproving noise power measurement as may be operative to reduce dynamicrange associated with power measurement or detection or other frequencyselective measurements employed therein.

Referring to an alternative embodiment 2400 of FIG. 24, another orsecond DAC (which may be operating at the same frequency or a differentfrequency as the primary/first DAC) is operated at (for example) lowerloading than the signal of interest DAC, and is input as the signalreference input of the noise canceller ahead of the power measurementfunction. By operating this second DAC at a lower loading and overallpower level, it is substantially absent the harmful spurious emissionstargeted by the synthesizer, and provides a means for the noisecanceller to reduce the signal-of-energy level prior to spuriousemissions power measurement, without unduly desensitizing the powermeasurement (or undoing the monotonicity of the power measurement).

As can be seen with respect to this diagram, one or more filters,scaling/gain, phase adjustment modules, functional blocks, circuitries,etc. may be optionally implemented before and/or after the second DAC.The controller may provide control to adjust any operational parameterof these modules, functional blocks, circuitries, etc.

As can be seen when comparing this diagram with the previous diagram, anadditional output from the modulator is used to drive the input of thesecond DAC, and a coupler need not be implemented between the first DACand the amplifier and/or filter. The output from the second DAC, whichmay optionally undergo certain processing as described above, isprovided as the signal reference input to the SOI (noise) canceller. Thesignal plus noise input, that is also provided to the SOI (noise)canceller, is provided from the coupler following the amplifier and/orfilter. After undergoing appropriate processing, the signal output fromthe SOI (noise) canceller is provided to the one or more powerdetectors.

In even other embodiments, the phase of the signal of interest producedfor the noise canceller noise reference input is adjusted (e.g., 180° orsome other adjustment amount). For example, the respective inputs to anysuch SOI (noise) canceller implemented with any given embodiment and/ordiagram, namely, the signal reference input, may undergo appropriateadjustment. It is also noted that the signal reference input provided tothe SOI (noise) canceller may be adjusted 180° only with respect to acertain frequency bandwidth (e.g., a particular portion of the frequencyspectrum or at a particular frequency). Generally speaking, negativephase will undergo increasing for a given amount of delay as thefrequency increases. Also, generally speaking, different portions of thefrequency bandwidth may undergo adjustment by different amounts (e.g., afirst portion undergoing adjustment by 180°, a second portion undergoingadjustment by 360°, a third portion undergoing adjustment by some othervalue, etc.).

In even other embodiments, the signal of interest produced for the noisecanceller noise reference input is adjusted so that it is delayed (oradvanced, when the input to the primary DAC is typically buffered)relative to the signal of interest path into the primary DAC. Byadjusting the relative delay and/or buffering amount between twosignal-of interest paths, a linear phase tilt (between the two signal ofinterest paths) is manifested. Such adjustment of the relative delayand/or buffering amount between the two respective signal of interestpaths may generally be applied to any of a number of different diagramsand/or embodiments presented herein. For example, with respect to FIG.24, if a delay and/or buffering is introduced in one of the paths, suchas between the modulator and the signal reference input that is providedto the SOI (noise) canceller, then appropriate delay and/or bufferingmay be needed within the other of the paths, such as between themodulator and the signal plus noise input that is provided to the SOI(noise) canceller. Analogously, with respect to FIG. 25, which isdescribed in additional detail below, the use of an adaptable delayadjuster, which may be under the control of the controller therein, maybe implemented to appropriate delay, alignment, synchronization, etc.between different respective paths within a given embodiment.

For measuring spurious power close to a 6 MHz signal of interest,manifesting a phase tilt due to relative delay differences correspondingto, for example, 180 degrees across a 6 MHz span, a one-tap noisecanceller can reduce signal of interest energy more than it will reducethe spurious energy adjacent to the signal of interest band. In evenother embodiments, leveraging relative delay of the two inputs to thenoise canceller bandpass filters are employed to help isolate the signalof interest and its adjacent spurious emissions band targeted formeasurement from signal of interest energy at more distant portions ofthe spectrum. For example, the one or more filters, which may befrequency selective or frequency tunable folders, may be implemented asone or more bandpass filters. For example, with respect to theembodiment 2300 and FIG. 23 in the embodiment 2400 and FIG. 24, the tworespective inputs to the SOI (noise) canceller, namely the signalreference input and the signal plus noise input, may undergo respectivebandpass filtering. With respect to the embodiment 2500 of FIG. 25,given the particular architecture and art apology thereof, the one ormore frequency tunable filters may be implemented as one or morebandpass filters such that the implemented one or more frequency tunablefilters therein will modify both of the respective paths with a common,singular filter (e.g., both of the respective signal reference input andthe signal plus noise input passed through the common, singular filter)

Referring to an alternative embodiment 2500 of FIG. 25, the analog tapin the noise canceller manifests phase adjustments via a controllable oradaptable delay adjuster, which may be implemented as a voltagecontrolled adjustable delay line. In one embodiment, with such anadjustable delay tap, the coupled-off signal of interest (e.g., whichmay be replete with spurious energy adjacent to a portion of the signalof interest spectrum), may be split (e.g., effectuated by a splitter)such that one of the paths passes through the controllable or adaptabledelay adjuster (e.g., an adjustable delay tap), and the delay isadjusted (along with a gain tap in one embodiment) to minimize the powerin the combination (e.g., effectually operated as a noise canceller).Since the two inputs to the noise canceller have similar phase acrosstheir respective frequency spectra, and since they are relativelyundelayed, the controllable or adaptable delay adjuster (e.g., anadjustable delay tap) will be operated to phase match (via itsrespective delay) the signal of interest to achieve the most cancelingpossible, and with a suitable starting delay difference in theadjustable delay device, the signal of interest will be reduced in thenoise canceller relative to the adjacent spurious emissions. In theseembodiments operating on the principle of phase tilt associated withdelay beating against a similar signal with flat phase, since the signalof interest energy is so much stronger than the spurious emissionslimit, the reduction of the signal of interest energy will dominate theconverged solution. It is noted that while accuracy in the powermeasurements is not critical (e.g., and as such, relatively lower end,less high-performing modules, functional blocks, circuitries, etc. maybe employed to effectuate such measurements), monotonicity to drive thegradient or dithering convergence is critical (e.g., based upon theoperation of the steepest descent and/or dithering operation),differentiating the requirements of this specialized power measurementfunction from commercial test equipment (e.g., commercially availablespectrum analyzers, off-the-shelf test equipment and/or other equipmentthat may be included within various housings, structures, laboratories,etc.).

Certain diagrams are presented and described below with respect tomethod steps. While certain of the respective method steps diagramsrelate to certain architectures, designs, layouts, etc. of variousmodules, functional blocks, circuitries, etc. as may be implemented inaccordance with several of the previous diagrams and/or embodiments, thereader will properly understand that analogous method steps may beassociated with an derived from any of the various architectures,designs, layouts, etc. of various modules, functional blocks,circuitries, etc. as may be implemented in accordance with several ofthe previous diagrams and/or embodiments. That is to say, any of thearchitectures, designs, layouts, etc. of various modules, functionalblocks, circuitries, etc. as may be implemented in accordance withseveral of the previous diagrams and/or embodiments may alternatively beunderstood in accordance with corresponding and respective method steps.

FIG. 26A, FIG. 26B, FIG. 27, FIG. 28A, and FIG. 28B are diagramsillustrating embodiments of methods 2600, 2601, 2700, 2800, and 2801,respectively, for operating one or more devices including at least onedigital to analog converter (DAC) therein.

Referring to method 2600 of FIG. 26A, the method 2600 begins byprocessing digital data thereby generating at least one codeword, asshown in the block 2610. In certain embodiments, the operations of theblock 2610 may be viewed as that which may be performed by a modulator.The method 2600 then continues by operating a digital to analogconverter (DAC) for processing the at least one codeword therebygenerating an analog signal, as shown in a block 2620.

The method 2600 then operates by synthesizing at least one distortionterm, based on the at least one codeword or a portion thereof,corresponding to a DAC operational characteristic, as shown in a block2630. For example, such a distortion term may be related to one or moreoperational characteristics of the DAC. Multiple different andrespective embodiments and/or diagrams are presented herein describingparticular characteristics associated with various DAC operationalcharacteristics. In some instances, the distortion synthesis isparticularly targeted in dealing with relatively low frequency spuriousadmissions the may be generated in accordance with him perfectivedigital to analog conversion. Alternatively, and other embodiments, suchdistortion synthesis may be particularly targeted in dealing withimproving transition band and/or stop the performance. In even otherembodiments, such distortion synthesis may be particularly targeted indealing with improving skirt and/or spectral mask performance. In yetother embodiments, such distortion synthesis may be particularlytargeted in improving various measurements including frequency selectivemeasurements (e.g., such as noise power or detection measurements) inaccordance with reducing the dynamic range associated with an input ofsuch modules, functional blocks, circuitries, etc. and/or test equipmentas may be implemented to effectuate such measurements. Generallyspeaking, in accordance with such synthesis of one or more distortionterms in accordance with the various diagrams and/or embodiments herein,such one or more distortion terms may be particularly targeted indealing with any one or more of the various operational modes asdescribed herein. That is to say, more than one given application may betargeted in accordance with calculating any one or more distortionterms.

The method 2600 then continues by employing the at least one distortionterm for reducing distortion associated with the analog signal, as shownin a block 2640. In certain, the operations of the blocks 2630 and 2640may be performed alternatively before the operation of a block 2620.That is to say, in certain situations, after the at least one distortionterm has been synthesized and after the one or more distortion termshave been used for reducing distortion, such as in accordance withcombining the at least one distortion term with the at least onecodeword, then the modified at least one codeword is provided to the DACthereby generating the analog signal. In addition, in certainembodiments, it is noted that the operation of the respective blocks areperformed substantially or approximately contemporaneously.

Referring to method 2601 of FIG. 26A, as can be seen, this diagram hassome similarities to the previous diagram. The method 2601 begins byprocessing digital data thereby generating at least one codeword, asshown in a block 2611. The method 2601 then continues by operating a DACfor processing the at least one codeword thereby generating an analogsignal, as shown in a block 2621.

Then, the method 2601 operates by synthesizing at least one distortionterm, based on the at least one codeword or portion thereof,corresponding to a DAC characteristic, as shown in a block 2631. Themethod 2601 continues by modifying the at least one distortion termbased on a frequency selective measurement corresponding to the analogsignal or least one additional signal derived therefrom, as shown in ablock 2641. For example, in some instances, the frequency selectivemeasurement is that of a frequency selective power measurement that ismade in the analog domain based on the analog signal or at least oneadditional signal derived therefrom. For example, the at least oneadditional signal derived therefrom may be a modified version of theanalog signal that may have undergone filtering including that by afrequency tunable filter.

The method 2601 then continues by employing the modified at least onedistortion term for reducing distortion associated with the analogsignal, as shown in a block 2651. As can be seen when comparing thisdiagram to the previous diagram, the at least one distortion term mayundergo modification based upon one or more frequency selectivemeasurements corresponding to the analog signal or at least oneadditional signal derived therefrom. As such, the method 2601 mayoutperform the method 2600 and certain situations given that additionalinformation is provided and used for generating the final/resultantdistortion term that is employed for reducing distortion associated withthe analog signal.

Referring to method 2700 of FIG. 27, the method 2700 begins byprocessing digital data thereby generating least one codeword, as shownin a block 2710. The method 2700 then continues by operating a DAC forprocessing the at least one codeword thereby generating a first analogsignal, as shown in a block 2720.

Then, the method 2700 operates by stop band filtering the first analogsignal thereby generating a filtered, first analog signal, as shown in ablock 2730. Based on the at least one codeword or a portion thereof, themethod 2700 operates by synthesizing at least one distortion termcorresponding to a frequency band of the first analog signal, as shownin a block 2740. After this at least one distortion term has beensynthesized, the method 2700 operates by modifying the at least onedistortion term based on one or more frequency selective measurementscorresponding to the filtered, first analog signal or at least oneadditional signal derived therefrom, as shown in a block 2750.

The method 2700 continues by operating a second DAC for processing themodified at least one distortion term thereby generating a second analogsignal, as shown in a block 2760. The method 2700 then operates bycombining the filtered, first analog signal and the second analog signalthereby reducing distortion associated with the first analog signal orthe filtered, first analog signal, as shown in a block 2770.

Referring to method 2800 of FIG. 28A, the method 2800 begins byprocessing digital data thereby generating at least one codeword, asshown in a block 2810. The method 2800 then continues by operating a DACfor processing the at least one codeword thereby generating an analogsignal, as shown in a block 2820. The method 2800 then operates bysynthesizing a plurality of distortion terms, based on the at least onecodeword or portion thereof, corresponding to at least one DACoperational characteristic, as shown in a block 2830.

The method 2800 then continues by narrowband filtering each of theplurality of distortion terms thereby generating a plurality of modifieddistortion terms, as shown in a block 2840. In certain situations, eachrespective narrowband filtering operation is applied to each respectiveone of the plurality of distortion terms, such that a first narrowbandfiltering associated with a first portion of the frequency spectrum isapplied to a first of the plurality of distortion terms, a secondnarrowband filtering associated with a second portion of the frequencyspectrum is applied to a second of the plurality of distortion terms,and so on.

The method 2800 operates by combining the plurality of modifieddistortion terms thereby generating a combined distortion term, as shownin a block 2850. The method 2800 continues by employing the combineddistortion term for reducing distortion associated with the analogsignal, as shown in a block 2860.

Referring to method 2801 of FIG. 28A, the method 2801 begins byprocessing digital data thereby generating at least one codeword, asshown in a block 2811. The method 2801 continues by operating a DAC forprocessing the at least one codeword thereby generating an analogsignal, as shown in a block 2821.

The method 2801 operates by coupling at least some of the analog signalthereby generating a signal reference input, as shown in a block 2831.The coupling of at least some of the analog signal may be effectuated bya coupler implemented after a DAC and before a subsequent amplifierand/or filter. The signal reference input may be one of at least twoinputs provided to a SOI (noise) canceller as may be understood withrespect to certain diagrams and/or embodiments herein.

The method 2801 continues by amplifying and/or filtering the analogsignal thereby generating a modified analog signal, as shown in a block2841. Subsequently, the method 2801 operates by coupling at least someof the modified analog signal thereby generating a signal plus noiseinput, as shown in a block 2851. The coupling of at least some of themodified analog signal they be effectuated by a coupler are implementedafter and amplifier and/or filter. The signal plus noise input may beanother one of at least two inputs provided to a SOI (noise) cancelleras may be understood with respect to certain diagrams and/or embodimentsherein.

The method 2801 operates by processing the signal reference input andthe signal plus noise input in accordance with SOI (noise) cancellationfor improving one or more noise power measurements corresponding to themodified analog signal or at least one additional signal derivedtherefrom, as shown in a block 2861.

Again, it is noted that while certain diagrams and/or embodiments ofmethod steps have been included herein, it is noted that any of thevarious architectures, designs, layouts, etc. of various modules,functional blocks, circuitries, etc. as may be implemented in accordancewith any of the several of the previous diagrams and/or embodiments mayproperly understand in accordance with analogous method steps as may beassociated with an derived from any of the various architectures,designs, layouts, etc. of various modules, functional blocks,circuitries, etc. as may be implemented in accordance with several ofthe previous diagrams and/or embodiments. Again, any of thearchitectures, designs, layouts, etc. of various modules, functionalblocks, circuitries, etc. as may be implemented in accordance withseveral of the previous diagrams and/or embodiments may alternatively beunderstood in accordance with corresponding and respective method steps.

With respect to the various diagrams and embodiments included herein, itis noted that, while certain generic terminology such as modulator, DAC,synthesizer, adapter, coupler, filter, power detector, controller, etc.are used among multiple diagrams, it is noted that each respectivediagram and embodiment may include such components having differentcharacteristics, operational parameters, etc. For example, the modulatorof one diagram and/or embodiment may not necessarily be identical to amodulator within another diagram and/or embodiment. That is to say,while the operation of modulation as performed by a modulator may begenerically similar within the two respective devices, any such tomodulators may operate in accordance with different characteristics,operational parameters, etc.

As at least one example, a first implementation of a modulator mayoperate in accordance with processing data having a first datacharacteristics (e.g., having a certain bit rate, a certain symbol rate,etc.) and generating codewords having first codeword characteristics(e.g., X number of bits per codeword, spanning a particular dynamicrange between a largest codeword and a smallest codeword or a largestnegative codeword, having a particular step between the respectivecodewords, etc.). Analogously, a second implementation of a modulatormay operate in accordance with processing data having second datacharacteristics that are different from those employed by the firstmodulator. Similarly, the different other respective componentsillustrated within the different respective guide diagrams and/orembodiments may also operate in accordance with differentcharacteristics, operational parameters, etc. As may be understood, aDAC of one diagram and/or embodiment may operate in accordance with afirst sampling frequency, a first output power, a first dynamic range,etc., while another DAC of another diagram and/or embodiment may operatein accordance with a second sampling frequency, a second output power, asecond dynamic range, etc. Generally speaking, while the genericfunctions and operations of components having a similar nomenclature aresimilar, the specific characteristics, operational parameters, etc. bywhich each is specifically implemented and operated may differ fromembodiment to embodiment.

As may be used herein, the terms “substantially” and “approximately”provides an industry-accepted tolerance for its corresponding termand/or relativity between items. Such an industry-accepted toleranceranges from less than one percent to fifty percent and corresponds to,but is not limited to, component values, integrated circuit processvariations, temperature variations, rise and fall times, and/or thermalnoise. Such relativity between items ranges from a difference of a fewpercent to magnitude differences. As may also be used herein, theterm(s) “operably coupled to”, “coupled to”, and/or “coupling” includesdirect coupling between items and/or indirect coupling between items viaan intervening item (e.g., an item includes, but is not limited to, acomponent, an element, a circuit, and/or a module) where, for indirectcoupling, the intervening item does not modify the information of asignal but may adjust its current level, voltage level, and/or powerlevel. As may further be used herein, inferred coupling (i.e., where oneelement is coupled to another element by inference) includes direct andindirect coupling between two items in the same manner as “coupled to”.As may even further be used herein, the term “operable to” or “operablycoupled to” indicates that an item includes one or more of powerconnections, input(s), output(s), etc., to perform, when activated, oneor more its corresponding functions and may further include inferredcoupling to one or more other items. As may still further be usedherein, the term “associated with”, includes direct and/or indirectcoupling of separate items and/or one item being embedded within anotheritem. As may be used herein, the term “compares favorably”, indicatesthat a comparison between two or more items, signals, etc., provides adesired relationship. For example, when the desired relationship is thatsignal 1 has a greater magnitude than signal 2, a favorable comparisonmay be achieved when the magnitude of signal 1 is greater than that ofsignal 2 or when the magnitude of signal 2 is less than that of signal1.

As may also be used herein, the terms “processing module”, “module”,“processing circuit”, and/or “processing unit” (e.g., including variousmodules and/or circuitries such as may be operative, implemented, and/orfor encoding, for decoding, for baseband processing, for modulating, forsynthesizing, for filtering, for digital to analog conversion, etc.) maybe a single processing device or a plurality of processing devices. Sucha processing device may be a microprocessor, micro-controller, digitalsignal processor, microcomputer, central processing unit, fieldprogrammable gate array, programmable logic device, state machine, logiccircuitry, analog circuitry, digital circuitry, and/or any device thatmanipulates signals (analog and/or digital) based on hard coding of thecircuitry and/or operational instructions. The processing module,module, processing circuit, and/or processing unit may have anassociated memory and/or an integrated memory element, which may be asingle memory device, a plurality of memory devices, and/or embeddedcircuitry of the processing module, module, processing circuit, and/orprocessing unit. Such a memory device may be a read-only memory (ROM),random access memory (RAM), volatile memory, non-volatile memory, staticmemory, dynamic memory, flash memory, cache memory, and/or any devicethat stores digital information. Note that if the processing module,module, processing circuit, and/or processing unit includes more thanone processing device, the processing devices may be centrally located(e.g., directly coupled together via a wired and/or wireless busstructure) or may be distributedly located (e.g., cloud computing viaindirect coupling via a local area network and/or a wide area network).Further note that if the processing module, module, processing circuit,and/or processing unit implements one or more of its functions via astate machine, analog circuitry, digital circuitry, and/or logiccircuitry, the memory and/or memory element storing the correspondingoperational instructions may be embedded within, or external to, thecircuitry comprising the state machine, analog circuitry, digitalcircuitry, and/or logic circuitry. Still further note that, the memoryelement may store, and the processing module, module, processingcircuit, and/or processing unit executes, hard coded and/or operationalinstructions corresponding to at least some of the steps and/orfunctions illustrated in one or more of the Figures. Such a memorydevice or memory element can be included in an article of manufacture.

The present invention has been described above with the aid of methodsteps illustrating the performance of specified functions andrelationships thereof. The boundaries and sequence of these functionalbuilding blocks and method steps have been arbitrarily defined hereinfor convenience of description. Alternate boundaries and sequences canbe defined so long as the specified functions and relationships areappropriately performed. Any such alternate boundaries or sequences arethus within the scope and spirit of the claimed invention. Further, theboundaries of these functional building blocks have been arbitrarilydefined for convenience of description. Alternate boundaries could bedefined as long as the certain significant functions are appropriatelyperformed. Similarly, flow diagram blocks may also have been arbitrarilydefined herein to illustrate certain significant functionality. To theextent used, the flow diagram block boundaries and sequence could havebeen defined otherwise and still perform the certain significantfunctionality. Such alternate definitions of both functional buildingblocks and flow diagram blocks and sequences are thus within the scopeand spirit of the claimed invention. One of average skill in the artwill also recognize that the functional building blocks, and otherillustrative blocks, modules and components herein, can be implementedas illustrated or by discrete components, application specificintegrated circuits, processors executing appropriate software and thelike or any combination thereof.

The present invention may have also been described, at least in part, interms of one or more embodiments. An embodiment of the present inventionis used herein to illustrate the present invention, an aspect thereof, afeature thereof, a concept thereof, and/or an example thereof. Aphysical embodiment of an apparatus, an article of manufacture, amachine, and/or of a process that embodies the present invention mayinclude one or more of the aspects, features, concepts, examples, etc.described with reference to one or more of the embodiments discussedherein. Further, from figure to figure, the embodiments may incorporatethe same or similarly named functions, steps, modules, etc. that may usethe same or different reference numbers and, as such, the functions,steps, modules, etc. may be the same or similar functions, steps,modules, etc. or different ones.

Unless specifically stated to the contra, signals to, from, and/orbetween elements in a figure of any of the figures presented herein maybe analog or digital, continuous time or discrete time, and single-endedor differential. For instance, if a signal path is shown as asingle-ended path, it also represents a differential signal path.Similarly, if a signal path is shown as a differential path, it alsorepresents a single-ended signal path. While one or more particulararchitectures are described herein, other architectures can likewise beimplemented that use one or more data buses not expressly shown, directconnectivity between elements, and/or indirect coupling between otherelements as recognized by one of average skill in the art.

The term “module” is used in the description of the various embodimentsof the present invention. A module includes a functional block that isimplemented via hardware to perform one or module functions such as theprocessing of one or more input signals to produce one or more outputsignals. The hardware that implements the module may itself operate inconjunction software, and/or firmware. As used herein, a module maycontain one or more sub-modules that themselves are modules.

While particular combinations of various functions and features of thepresent invention have been expressly described herein, othercombinations of these features and functions are likewise possible. Thepresent invention is not limited by the particular examples disclosedherein and expressly incorporates these other combinations.

What is claimed is:
 1. An apparatus, comprising: a modulator forprocessing digital data thereby generating at least one codeword; afirst digital to analog converter (DAC) for processing the at least onecodeword thereby generating a first analog signal; a stop band filterfor filtering the first analog signal thereby generating a filtered,first analog signal; a synthesizer for providing at least one distortionterm, based on the at least one codeword or a portion thereof and acontrol signal, corresponding to a frequency band of the first analogsignal; an adapter for modifying the at least one distortion term basedon at least one frequency selective measurement corresponding to thefiltered, first analog signal or at least one additional signal derivedthere from; a second DAC for processing the at least one distortion termthereby generating a second analog signal; a combiner for combining thefiltered, first analog signal and the second analog signal therebyreducing distortion within the filtered, first analog signal therebygenerating a combined signal; and a controller for generating thecontrol signal in accordance with dithering operations based on ameasurement associated with the combined signal.
 2. The apparatus ofclaim 1, further comprising: an up-converter for processing the secondanalog signal before providing it to the combiner.
 3. The apparatus ofclaim 1, further comprising: a coupler for outputting at least a portionof a combined signal output from the combiner; a frequency selectivefilter for selecting a spectral band component of the at least a portionof the combined signal; a power detector for measuring power of thespectral band component; and wherein: the controller for generating thecontrol signal based on the measured power of the spectral bandcomponent.
 4. The apparatus of claim 1, wherein: the first DAC operativeat a first frequency; and the second DAC operative at a secondfrequency.
 5. The apparatus of claim 1, wherein: the synthesizer forgenerating the at least one distortion term in real time based on the atleast one frequency selective measurement or at least one additionalfrequency selective measurement.
 6. The apparatus of claim 1, wherein:the adapter for performing adaptive at least one of filtering, gain,phase, and delay adjustment of the at least one distortion term.
 7. Theapparatus of claim 1, wherein: the apparatus being a communicationdevice operative within at least one of a satellite communicationsystem, a wireless communication system, a wired communication system,and a fiber-optic communication system.
 8. An apparatus, comprising: amodulator for processing digital data thereby generating at least onecodeword; a first digital to analog converter (DAC), operating at afirst frequency, for processing the at least one codeword therebygenerating a first analog signal; a stop band filter for filtering thefirst analog signal thereby generating a filtered, first analog signal;a synthesizer for providing at least one distortion term, based on theat least one codeword or a portion thereof, corresponding to a frequencyband of the first analog signal; an adapter for modifying the at leastone distortion term based on at least one frequency selectivemeasurement corresponding to the filtered, first analog signal or atleast one additional signal derived there from; a second DAC, operatingat a second frequency, for processing the modified at least onedistortion term thereby generating a second analog signal; and acombiner for combining the filtered, first analog signal and the secondanalog signal thereby reducing distortion within the filtered, firstanalog signal.
 9. The apparatus of claim 8, further comprising: anup-converter for processing the second analog signal before providing itto the combiner.
 10. The apparatus of claim 8, further comprising: anamplifier for processing the first analog signal before providing it tothe stop band filter.
 11. The apparatus of claim 8, further comprising:a coupler for outputting at least a portion of a combined signal outputfrom the combiner; a frequency selective filter for selecting a spectralband component of the at least a portion of the combined signal; a powerdetector for measuring power of the spectral band component; and acontroller for directing operation of the adapter based on the measuredpower of the spectral band component.
 12. The apparatus of claim 8,wherein: the synthesizer for generating the at least one distortion termin real time based on the at least one frequency selective measurementor at least one additional frequency selective measurement.
 13. Theapparatus of claim 8, wherein: the adapter for performing adaptive atleast one of filtering, gain, phase, and delay adjustment of the atleast one distortion term.
 14. The apparatus of claim 8, wherein: theapparatus being a communication device operative within at least one ofa satellite communication system, a wireless communication system, awired communication system, and a fiber-optic communication system. 15.A method, comprising: processing digital data thereby generating atleast one codeword; operating a first digital to analog converter (DAC)for processing the at least one codeword thereby generating a firstanalog signal; stop band filtering the first analog signal therebygenerating a filtered, first analog signal; synthesizing at least onedistortion term, based on the at least one codeword or a portionthereof, corresponding to a frequency band of the first analog signal;modifying the at least one distortion term based on at least onefrequency selective measurement corresponding to the filtered, firstanalog signal or at least one additional signal derived there from;operating a second DAC for processing the modified at least onedistortion term thereby generating a second analog signal; and combiningthe filtered, first analog signal and the second analog signal therebyreducing distortion within the filtered, first analog signal.
 16. Themethod of claim 15, wherein: operating the first DAC at a firstfrequency; and operating the second DAC at a second frequency.
 17. Themethod of claim 15, further comprising: coupling at least a portion of acombined signal generated from the combination of the filtered, firstanalog signal and the second analog signal; performing frequencyselective filtering for selecting a spectral band component of the atleast a portion of the combined signal; measuring power of the spectralband component; and modifying the at least one distortion term based onthe measured power of the spectral band component.
 18. The method ofclaim 15, further comprising: generating the at least one distortionterm in real time based on the at least one frequency selectivemeasurement or at least one additional frequency selective measurement.19. The method of claim 15, wherein: the modifying the at least onedistortion term in accordance with performing adaptive at least one offiltering, gain, phase, and delay adjustment of the at least onedistortion term.
 20. The method of claim 15, wherein: the methodperformed within a communication device operative within at least one ofa satellite communication system, a wireless communication system, awired communication system, and a fiber-optic communication system.